A rainbow for everyone

Traffic lights for everyone

Stephen Westland of Colour chat recently posted about a clever new LED traffic light developed in Japan. Here’s my tweet with the link to Westland’s original blog post:

I really like the idea of making a traffic light that works for everyone: for people with full color vision and people with color vision deficiencies. In fact, I think we should do the same with our color palettes. Why do I say that?

A rainbow for everyone

Take a look at  Figure 1 below. This is a map of the Bouguer Gravity (terrain corrected Bouguer Gravity to be precise)  in Southern Tuscany, colored using a rainbow palette. I intentianally left out the colorbar. For a moment ignore the sharp gradient changes at the yellow and cyan color (that is one of the topics of my upcoming series “The rainbow is dead…long live the rainbow!”). Can you tell which color is representing high values an which low? If you have used a mnemonic like ROY B GIV and can tell that highs are towards the Southwest and lows towards the Northeast, then you are right and you also have full color vision, just like me. Great, because this post is exacly for us, the “normals”.

Figure 1

Take now a look at Figure 2:

this is exacly the same map, but I run a simulation to show us normals how it would be seen by a person with Deuteranopia, a form of color vision deficiency (I run the simulation using Vischeck plugin for ImageJ, see the related contents section). Can you tell now which is high and which is low? I certainly can, but I’d be wrong. Using topography as a methafor, what I see is a nice yellow mountain ridge, from which the surface slopes down to shades of brown, and then white, on either side. There’s a nice big blue lake in the the Northeast but as far as I’m concerned there’s also a low in the South.

Figure 2

In my upcoming seires “The rainbow is dead…long live the rainbow!” i will tackle these topics in depth and I will also propose some new rainbow-like color palettes that are better for everyone, no matter how many and how well you see colors. Stay tuned!


Is Indigo really a colour of the rainbow?

Why is the hue circle circular at all?


Color Blind Essentials eBook


Vischeck simulations using ImageJ plugin

Vischeck simulations online