Tips for designing scientific figures for color blind readers

color blindness scientific publishing

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Experience the world through a color blind lens

Everybody knows a color blind person. Everybody knows Mark Zuckerberg, he’s color blind. Or Bill Clinton, or Keanu Reeves, or… Color vision deficiencies are very common and affect a substantial portion of the population. As many as 8% of men and 0.5% of women are affected with the common form of red-green color blindness. Think about it, in a country like the United States, this means more than 13 million people (4.25% of the entire population), most of whom are male.

It is important to be aware of these data the moment you start designing your next figure for your research publication. The aim should always be to make the information we present as accessible as possible for our readers. It is a no-brainer that many of your readers will be color blind, the statistics don’t lie. But even before your manuscript reaches your public, the chance that it is reviewed by a color blind expert is substantial.

Picking the right colors for your next figure is a must. In this article I’ll go over some tips and tricks that will help you to make your graphics accessible for your color blind peers.

Color blindness is actually bad terminology. There is only a very small portion of the population that sees everything in black and white (monochromatic vision). Color blind people usually have a reduced ability to distinguish shades of certain colors. Better terminology could be color vision impaired or something similar.

So, when choosing a color scheme for your scientific figures, it helps to know which shades are difficult to distinguish for your color blind readers. Most commonly reds and greens give problems, as shown in the picture below, but also blues and yellows might be difficult to distinguish for some people.

red green normal vision

This is how non-color blind people see green & red


red green colorblind vision

This is how color blind people see green & red

It is obvious that you should avoid these colors in designing your scientific figures. But there are more approaches you could follow to avoid the color blindness pitfall:

  • Avoid lesser-known bad color combinations: green & brown, blue & purple, green & blue, light green & yellow, blue & grey, green & grey, green & black;
  • Don’t use color combinations at all, but work with different shades of the same color. In other words make your figures monochrome;
  • Use a high enough contrast. Contrast is something that most color blind people still can perceive very well;
  • Use textures instead of colors;
  • If you want to signal emotions with color (red = bad, green = good), consider adding another symbol or graphical element with the same meaning (might be even text).

It helps to be aware of these tips that can make your figures more readable for color blind people, but it is certainly not a surefire way for optimal figures. There is a substantial risk that your figures will not look very harmonic and balanced anymore when you apply these principle on the fly. An alternative approach is to define a color scheme upfront, one that certainly will work for color blind people too.

A good way to start is this color blind safe palette. For most applications this will be sufficient.

color-blindness- color palette

This 15-color palette provides good discrimination for common color blindness types. Individuals with tritanopia cannot distinguish colors marked with ● and ◥. source: http://mkweb.bcgsc.ca/biovis2012

 

However, if you’ll need more artistic freedom I advise you to use simulations to make your color choices. There are many tools that can tell you how your design would look like to a color blind eye. Here are my favorites:

  • Color Oracle: a free color blindness simulator that you can install on your computer. It applies a full screen color filter, so you can see in real time how a color blind person would see your design.
  • If you use Adobe Photoshop or Adobe Illustrator you can simulate color blindness by creating a proof. Just go to View > Proof Setup > Color Blindness.
proof setup photoshop

Proof setup in Photoshop

One question that mainly cell biologists have when discussing this matter is what to do with colored fluorescent images. Red-green color coding is very widespread in the life sciences field, but far from optimal for effective communication. There are a few easy considerations to make next time you work with fluorescent images:

  • Do you need color to represent your data? Various shades of grey are easy to detect by the human eye. It might even be easier to see details in black and white images.
  • You can replace red with magenta. In Photoshop you can copy the contents of the red channel and paste them into the blue channel (Window > Channels)
immunofluorescence color blind

Red-green color coding in an immunofluorescent image. (a) Conventional color coding is difficult for individuals with red-green color blindness (protanopia or deuteranopia) to discriminate. (b) Replacing red with magenta (top) or green with turquoise (bottom) improves visibility for such individuals. Nat Methods. 2011 Jun;8(6):441.

Hope these tips and advice will stimulate you to take action and optimize your future figures also for your color blind readers. They will notice it and will be grateful. Believe me.

P.S. If you happen to be color blind and you find it difficult to understand a figure due to bad color choices this might be useful: Visolve. It is assistive software for color blind people. Visolve uses filters to allow better discrimination of colors by making them lighter and/or darker, or increase the saturation.

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