The Rainbow Color Map (2023)

(31 May 2014)

The aim of this article is to explain why the rainbow color map is not the best one can chooseto represent physics data in pseudo color and to propose better solutions. It was writtenby Bernice Rogowitz (Visual Perspectives) and Olivier Couet (CERN).

To introduce this topic, we will describe the work we did on the candidate Higgs boson data.In this experiment, two specially-constructed beams of particles were set to collide infront of a particle detector, tuned to measure the energy emitted by the decay of thehypothesized Higgs Boson. Hundreds of trillions of collisions were analyzed to extractthe signature of the Higgs Boson, which was predicted to have a mass between 125 and127 GeV/C2 (Giga Electron Volts). The data represented in the four panels belowis the distribution of electron volts across the particle sensor.

Figure 1: This figure shows four different representations of the candidate Higgs-Boson data. The top left shows a rainbow colormap applied to the voltage data. In the bottom left, the analyst introduced a logarithmic transform to the data, to better reveal variations at the low end of the range. In the bottom right, the rainbow colormap was replaced with a “perceptual” colormap, so that equal magnitude changes in the data would look like equal steps, perceptually. Finally, in the top right, the voltage values were also represented as a 3-D surface, so that the rapid variations at the low-end of the range could be better appreciated.

Rainbow Color


The rainbow color map is named that way because it goes through all the rainbow’s colors.The lower values are in the deep blue range and the higher values in the reds. In between it passestrough light blue green, yellow, orange … It is used as a default in many visualization systems sinceit is easy to calculate (it is a linear interpolation between (0,0,255) and (255,0,0) in RGB color space),and because the bright colors are visually appealing.

(Video) Don't Use the Rainbow Color Map


As it is explain in several visualisation articles the rainbow color map can be misleadingwhen visualising data. The main issues with this kind of color map are:

  1. It is confusing because it doesn’t have a monotonic perceptual ordering,
  2. structures in the data can be hidden, since not all data variations are represented visually,
  3. the fact the luminance is not controlled can hide data,
  4. it introduces gradients not related to the data,
  5. it artificially divides the data into a small number of categories, one for each color.

Despite these problems the color map is still the most widely used in pseudo-color representations.May be just because “it looks nice”. The following picture is a very good example showinghow misleading the color map can be. These two images represent the same data set. The oneon left uses a rainbow color map whereas the one on right uses a more appropriate map. Itis amazing to see how the rainbow map hides the well known structure of the Florida coastline. This is because all the values between 500m below sea level to 500m above sea levelare all painted the same color yellow. When the color map explicitly delineates sea level,the coastline is visible. Also, because the luminance of the colormap varies monotonicallyabove and below sea level, structures which were hidden by the Rainbow colormap become apparent,such as the Continental shelf and the Appalachian mountains. In this example, the coastline ofFlorida is very familiar. But in many cases, an analyst examines a visualization to discoverfeatures. Using the Rainbow colormap can distort the perception of these features and bevery misleading

Figure 2: These two panels show the same data, but with different colormaps. On the left, the “Rainbow” colormap provides a very colorful and vibrant image, however, it masks significant features in the data, and emphasizes less important ones. The “Perceptual” colormap in the right panel explicitly identifies the “0” in the data, which is sea level, and provides monotonic luminance variations above and below zero. This colormap provides a more faithful representation of the structures in the data. This tutorial shows how to produce a perceptual palette in ROOT.

Color maps in High Energy Physics

The rainbow is used a lot in High Energy Physics. On 2012, July 4th physics results showing the evidence of a new boson compatiblewith the Higgs boson signature were presented by the LHC experiments. Several plots usingrainbow color maps were shown. On all of them the results were very clear, and were cross-checked by all kinds of other representations like bar charts or contour plots. Neverthelesswe will see in this page how better color maps could have been used.

How the rainbow color map can mask structure in the data

With this color map, structures within the [0.1, 0.2] and [0.3, 0.6] ranges are invisible.The rule should be that equal steps in data value should correspond to equal perceptualsteps. The rainbow color map does not preserve intervals in data. The data are “interval”;the representation is “ordinal”.


The histogram presented on this plot does not have a lot of bins and there no possibilitiesto hide any structure in the two “blind ranges”. Fortunately alternative visualisationtechniques allow to bypass this issue.

From a rainbow color map plot to a more meaningful one

The data used for this exercise are from the CMS experiment. They show the boson mass at 125GeV. The basic macro used to produce the plots is the following. It simply attached thedata file mass_scan_maps_th2.root, define a palette and draw the histogram mass_scan_2d_hzz_th2using this palette.

{ TFile f("mass_scan_maps_th2.root"); mass_scan_2d_hzz_th2->SetContour(100); // Define color map gStyle->SetPalette(55); // Draw the histogram as a color plot mass_scan_2d_hzz_th2->Draw("colz");}

This histogram has more bins than the previous example, playing on them with various colormapwill be more interesting.

Rainbow color map in linear scale

The rainbow color map on the “Higgs data” gives the next output. They data look prettycontinuous, so we probably won’t find any surprising structures, but we might get more visualinsight into the shape of the continuous variation.The gradians artefacts in are clearly visible. in the light blue, yellow and red part of the map

Dark Body Radiator color map in linear scale

This color map does not have the problems we saw on the previous plot. To obtain it is ROOTit is enough to do:

(Video) Rainbow Friends Dr. Livesey Walk


The plot still looks continuous, but we do not have the gradians artefacts we saw with therainbow color map.

We should now try to make more evident the data structure in the continuous areas in thelower part of the color map.

Rainbow color map in logarithmic scale

To make more visible the structure in the lower part of the color map, we go into logarithmicscale along the Z axis. This works very well and we can clearly see the spot at 125 GeV.

But as we are back to the rainbow color map the artefact reappear. And we can see “rings”(in particular in the yellow range) which do not have any significance regarding the data set.

Dark Body Radiator color map in logarithmic scale

Going back to the Dark Body Radiator the “rings” disappear and we a back to a continuousgradation of tones, and, thanks to the logarithmic scale, the spot at 125 GeV is stillclearly visible.

(Video) NASCONDIAMOCI da BLU su ROBLOX!! | Rainbow Friends

Surface plot with a Dark Body Radiator color map in logarithmic scale

Finally going to a 3D surface makes the spot even more obvious ! The root command to obtainthis surface is:


Another Example

This case demonstrate the use of different colormaps for low- and high- spatial frequencydata set.

The image below shows four surfaces expressing the ozone level over the south pole. Therainbow colormap (left top) is compared with a luminance map (top right), which is great forshowing high spatial frequency detail. The bottom left shows a saturation map, where redand green increase in saturation from yellow at the midpoint of the data. This is greatfor displaying low spatial-frequency variations. The bottom right shows both a luminanceramp and a saturation scale, together, which reveals both low- and high-spatial frequencyinformation.

Figure 3: Four different colormaps are explored in this figure showing ozone levels in the southern hemisphere. The top-left panel shows the rainbow colormap. The top-right panel demonstrates how well a luminance-based colormap represents high-spatial-frequency (detailed) information. The bottom-left panel demonstrates how well a saturation-based colormap reveals low-spatial-frequency information. Combining luminance and saturation produces colormap that communicates both low and high-spatial frequency information, and may be a good candidate for a new default colormap. Source: Rogowitz, B.E. and Treinish, L.A., “Data Visualization: The End of the Rainbow” IEEE Spectrum 35, Issue 12, pp. 52-59, 1998.


What is a rainbow colormap? ›

Definition. The rainbow color map is named that way because it goes through all the rainbow's colors. The lower values are in the deep blue range and the higher values in the reds. In between it passes trough light blue green, yellow, orange …

Which of the following are issues with the rainbow colormap? ›

The main problem with the rainbow colour map is that it is not perceptually uniform. This means that equal steps in data values do not map to equal steps in perceived colour. As a result, fine details in the data are obscured and users can find it difficult to compare values.

What acronym can be helpful in remembering the colors of the rainbow? ›

ROYGBIV is an acronym for the sequence of hues commonly described as making up a rainbow: red, orange, yellow, green, blue, indigo, and violet.

What does a color map show? ›

A color map is a set of values that are associated with colors. Color maps are used to display a single-band raster consistently with the same colors. Each pixel value is associated with a color, defined as a set of red, green, and blue (RGB) values.

What color is Japanese Laurel? ›

Aucuba japonica

japonica is a rounded, evergreen shrub with small, reddish purple flowers in spring, and red berries (on female plants) in fall.

What is Jet Colormap? ›

c = jet returns the jet colormap as a three-column array with the same number of rows as the colormap for the current figure. If no figure exists, then the number of rows is equal to the default length of 256. Each row in the array contains the red, green, and blue intensities for a specific color.

What is wrong with using the rainbow color map for gradient visualization? ›

Another issue with an uneven colour palette like rainbow is that data presented using these colours may be unreadable or inaccurate for people with a vision deficiency or colour blindness. Colour maps that include both red and green colours with similar lightness cannot be read by a large fraction of the population.

How do color blind people see rainbow? ›

20. To the normally sighted person, a rainbow features all the colors of the rainbow. For many color blind people, however, a rainbow only appears to have 2 or 3 colors: blue and yellow.

Is Turbo colorblind friendly? ›

It seems turbo is distinguishable and smooth for all types of color blindness conditions, except Achromatopsia (total color blindness).

What is the acronym of rainbow? ›

"ROY G. BIV" is an acronym for the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet.

What are the 7 rainbow colours in order? ›

This sequence of colours gives us the characteristic pattern we're all familiar with, and that we learn from childhood through the use of mnemonic phrases. The colours of the rainbow are Red, Orange, Yellow, Green, Blue, Indigo and Violet.

How do you memorize the rainbow song? ›

ROY G BIV | The Colors of the Rainbow | Jack Hartmann - YouTube

What are the 5 colors on a map? ›

Colors on a Topo Map
  • Red: Overprinted on significant primary and secondary roads. ...
  • Black: Manmade or cultural features.
  • Blue: Water-related features.
  • Brown: Contour lines and elevation numbers.
  • Green: Vegetation features. ...
  • White: Sparse or no vegetation. ...
  • Purple: Revisions that have been made to a map using aerial photos.
27 Feb 2008

How many colors are on a map? ›

The four-color theorem states that any map in a plane can be colored using four-colors in such a way that regions sharing a common boundary (other than a single point) do not share the same color.

How do you read a map? ›

How to read a map - YouTube

Is Laurel a tree? ›

Prunus laurocerasus

Cherry laurel, also called English laurel, is a large evergreen shrub or small tree often used for landscaping, usually as a hedge.

Can you root aucuba in water? ›

Aucuba is a lovely shrub that seems to almost glitter in the shade. Propagating aucuba cuttings is a snap. In fact, aucuba is one of the easiest plants to grow from cuttings. It roots readily in rooting medium or a jar of water, and you won't need rooting hormones or an expensive misting system.

Why do aucuba leaves turn black? ›

As shade-loving plants, aucubas often develop black foliage when they receive too much sun. Sunburn appears as brown or black leaf blotches. Damage is heaviest on plants in dry soil and bright afternoon sun.

Is viridis a good colormap? ›

The “viridis” and “magma” scales do better - they cover a wide perceptual range in brightness in brightness and blue-yellow, and do not rely as much on red-green contrast. They do less well under tritanopia (blue-blindness), but this is an extrememly rare form of colorblindness.

How do you set a color plot in Matlab? ›

The following are the letters you can add to your code to control the color of your plot while plotting in Matlab.
  1. b blue.
  2. g green.
  3. r red.
  4. c cyan.
  5. m magenta.
  6. y yellow.
  7. k black.
  8. w white.

What is a perceptually uniform colormap? ›

Sequential colormaps (that are perceptually uniform of course) are basic colormaps that start at a reasonably low lightness value and uniformly increase to a higher value. They are commonly used to represent information that is ordered.

Why are rainbow color scales bad? ›

The first problem is that the rainbow colors do not follow any natural perceived ordering. Although the order of the hues can be learned, there is no innate sense of higher or lower [25]. The second problem is that the perceptual changes in the rainbow colors are not uniform.

Why is a rainbow colormap generally considered a poor option for ordered data? ›

Even though most people aren't colorblind, rainbow color schemes can be confusing because there's no clear “greater than” or “less than” logic to ordering the colors, warn computer science researchers David Borland and Russell M. Taylor II.

Why you should not use jet colormap? ›

This is not the case with the rainbow or the Jet colormaps. They have distinct bright and dark stripes within the number range, making them the wrong choice to encode numerical data. The situation is even worse for people with impaired color vision.

What are the 7 types of color blindness? ›

The three different types of color blindness are monochromatism, dichromatism, and anomalous trichromatism. Dichromatism and anomalous trichromatism can be distinguished even further by three types of malfunctioning cones: tritanopia (blue light), deuteranopia (green light), and protanopia (red light).

Why do I see GREY as green? ›

Sleep researchers have observed a strange phenomenon that occurs the longer we stay awake. Over the course of the day the color gray starts to appear greenish. Sleep reverses the effect and the next morning gray looks like gray again.

What colors do colorblind not see? ›

There are different types of colour blindness and in extremely rare cases people are unable to see any colour at all, but most colour blind people are unable to fully 'see' red, green or blue light.

Are more men color blind? ›

Since it's passed down on the X chromosome, red-green color blindness is more common in men. This is because: Males have only 1 X chromosome, from their mother.

What color is best for color blind? ›

Don't forget about people with complete color blindness and remember that 100% best colors for colorblind are black and white. So if your visualization works in greyscale you should be safe. Another advantage of using black and white data visualization is that they're print-ready.

What colour is best for colour-blind people? ›

Use a colour-blind-friendly palette when appropriate

For example, blue/orange is a common colour-blind-friendly palette. Blue/red or blue/brown would also work. For the most common conditions of CVD, all of these work well, since blue would generally look blue to someone with CVD.

What do the colors of the rainbow symbolize? ›

Each of the original eight colours represented an idea: pink for sexuality, red for life, orange for healing, yellow for sun, green for nature, blue for art, indigo for harmony, and violet for spirit. Before becoming synonymous with fabulous pride movements, the rainbow flag has stood for many social movements.

How many colours exist? ›

It has been determined by people who determine such things that there are somewhere around 18 decillion varieties of colors available for your viewing enjoyment. That's an 18 followed by 33 zeros.

What are the 12 rainbow colors? ›

The colors of the rainbow in order are red, orange, yellow, green, blue, indigo, violet. You can remember them with the acronym Roy G Biv! At one point or another, we have all seen a rainbow. But, although they are fairly common occurrences, it is remarkable how little most people actually know about rainbows.

Do Rainbows have pink? ›

Purple, magenta, and hot pink, as we know, don't occur in the rainbow from a prism because they can only be made as a combination of red and blue light. And those are on opposite sides of the rainbow, nowhere near overlapping. So there is no purple or hot pink in the rainbow from a prism.

Is indigo blue or purple? ›

Indigo is a rich color between blue and violet on the visible spectrum, it's a dark purplish blue. Dark denim is indigo as is Indigo dye. It's a cool, deep color and also a natural one.

Does the rainbow have an end? ›

So if you're on the ground, however far you walk, the end of the rainbow will always look as if it were on the edge of the horizon. But what people don't realise is that rainbows are actually complete circles, and obviously a circle has no end. You never see the whole circle because the earth's horizon gets in the way.

Where does pink go in ROYGBIV? ›

Since pink is not in a traditional rainbow, it can be tricky to place in the color wheel. Think of your pinks as rosy pinks (cool pinks, above left) and peachy pinks (warm pinks, above right). Rosy pinks should go between purple and red, while peachy pinks are best between red and orange.

Where does white and black fall in ROYGBIV? ›

And they found that as languages develop differing names for colors, those names always enter the language in the same order. So that order is black, white, red, green and yellow, blue, and then brown.

Is ROYGBIV a real person? ›

2012 - Roy G. Biv is a Real Live Person — New Hampshire Dance Institute.

What is a map color for school? ›

What most parents don't realize is that the phrase is just another term for regular colored pencils. Described as map pencils because of their use in the classroom, these coloring tools come in a variety of brands, sizes and quantities, to fit any supply need.

How do I choose a map color? ›

The trick is to pick a really nice color theme so your map looks great. You can also accent particular aspects of your data by your choice of color. For example, one strong dark color among a group of lighter colors will 'pop' out of the map, highlighting that particular facet of your data against all others.

What is pink on a map? ›

Areas or markers that are pink are public services open to the public. Train stations, hospitals, etc. It also includes underground pedestrian corridors. Underground pedestrian corridors are the light pink.

What color is a map? ›

Dark green usually represents low-lying land, with lighter shades of green used for higher elevations. In the next higher elevations, physical maps often use a palette of light brown to dark brown. Such maps commonly use reds, white, or purples to represent the highest elevations shown on the map.

Who Solved the 4 color problem? ›

The four-colour problem was solved in 1977 by a group of mathematicians at the University of Illinois, directed by Kenneth Appel and Wolfgang Haken, after four years of unprecedented synthesis of computer search and theoretical reasoning.

Which colour means what? ›

Red: Passion, Love, Anger. Orange: Energy, Happiness, Vitality. Yellow: Happiness, Hope, Deceit. Green: New Beginnings, Abundance, Nature.

What are the 4 steps of reading a map? ›

There are four key elements to reading a map:
  1. Choosing the right map.
  2. Understanding map symbols.
  3. Relating the map to the land.
  4. Orientating your map.
21 Jun 2022

Is reading a map hard? ›

And contrary to popular belief, it isn't particularly difficult. Once you understand what key markers like scale, longitude and latitude, and topographical lines mean, you'll be able to travel just about anywhere with a few quick calculations.

What is called map? ›

A map is a symbolic representation of selected characteristics of a place, usually drawn on a flat surface. Maps present information about the world in a simple, visual way. They teach about the world by showing sizes and shapes of countries, locations of features, and distances between places.

How do you remember colors? ›

The first letter of every word in the phrase is the first letter of all the different colours in the rainbow:
  1. Red (Richard)
  2. Orange (of)
  3. Yellow (York)
  4. Green (gave)
  5. Blue (battle)
  6. Indigo (in)
  7. Violet (vain)

What is the acronym used to remember visible light as seen when a rainbow appears in the sky? ›

The name "Roy G. Biv" is an easy way to remember the colors of the rainbow, and the order in which they appear: red, orange, yellow, green, blue, indigo, and violet.

How do you teach the colors of the rainbow? ›

Preschool Learning Colors with Rainbows on Tea Time with Tayla

What is ROYGBIV and what does it stand for? ›

"Roy g biv" is a mnemonic that helps you remember the order of the colors of the rainbow. So it's red, orange, yellow, green, blue, indigo and violet. On the number of colors in the rainbow. There aren't actually, strictly speaking, seven colors in the rainbow.

What color is the brain? ›

The brain is a pinkish, grayish color, and that's thanks to the parts that compose it. Most of the brain is made of cells called grey matter that are, in fact, gray.

Which color is best for memory? ›

Red boosted performance on detail-oriented tasks such as memory retrieval and proofreading by as much as 31 per cent compared to blue. Conversely, for creative tasks such as brainstorming, blue environmental cues prompted participants to produce twice as many creative outputs as when under the red colour condition.

What color will you remove in rainbow? ›

Today, many colour theorist argue that indigo should be removed from the rainbow. Like mentioned earlier, distinguishing between blue, violet, and indigo is rather difficult for the human eye. In fact, Newton only had seven colours in his spectrum because he thought the number had cosmic significance.

What is a rainbow without rain called? ›

One of the main ways a rainbow can form without any rain is called virga. The rainbow formed due to rain but the rain evaporated before it hit the ground.

What is a full circle rainbow called? ›

A full circle rainbow is called a 'glory'. Sky conditions have to be just right for it to happen and and even if they are, the bottom part of a full-circle rainbow is usually blocked by the horizon. NASA defines a glory an optical phenomenon that "looks like small, circular rainbows of interlocking colors."

Is there an end to a rainbow? ›

So if you're on the ground, however far you walk, the end of the rainbow will always look as if it were on the edge of the horizon. But what people don't realise is that rainbows are actually complete circles, and obviously a circle has no end. You never see the whole circle because the earth's horizon gets in the way.

How do you explain a rainbow to a child? ›

How Is A Rainbow Formed | The Dr. Binocs Show | Learn Videos For Kids

What is rainbow colour for kids? ›

From inside to outside, the colors of a rainbow are violet, indigo, blue, green, yellow, orange, and red.

How do I teach my child the rainbow? ›

Light Fantastic: 5 Ways to Teach with Rainbows
  1. Learn about rainbows (with both sides of your brain). Rainbows can teach us so much about science—and a lot about feelings, too. ...
  2. Go “rainbow hunting.” ...
  3. Bring the rainbow inside. ...
  4. Make your own rainbow. ...
  5. Make some rainbow-inspired art.

Where does pink go in ROYGBIV? ›

Since pink is not in a traditional rainbow, it can be tricky to place in the color wheel. Think of your pinks as rosy pinks (cool pinks, above left) and peachy pinks (warm pinks, above right). Rosy pinks should go between purple and red, while peachy pinks are best between red and orange.

Where does white go in ROYGBIV? ›

Embrace ROY G BIV.

When organizing by color, look to the rainbow. Walker recommends this method as you sort: "Start with white, cream, pink, red, orange, yellow, green, blue, indigo, violet, brown, gray, and black," she says.

What are the 12 rainbow colors? ›

The colors of the rainbow in order are red, orange, yellow, green, blue, indigo, violet. You can remember them with the acronym Roy G Biv! At one point or another, we have all seen a rainbow. But, although they are fairly common occurrences, it is remarkable how little most people actually know about rainbows.


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