Color Blindness

6% of the male population cannot read the number 49 in this image:

but yet people use red and green to differetiate areas in Google Earth. Here's a screen shot from a well promoted Google Earth project that shall remain nameless to save blushes.


A long time ago I reported talking to a Googler who couldn't even see the borders in this view.

There are a few rules of thumb to help with avoiding color blindness problems in maps:

• If you want to deliniate features using color, choose blends of yellow or blue, very few people have problems with identifying these colors.
• Convert your colors to gray scales, if there is a tonal difference color blind users can still differentiate by tone.
• Think of using different textures to mark areas. Unfortunately this isn't easy to do in Google Earth.

I'm doing some background reading at the moment and apparently color blindness is easily coped for by other features of our vision such as being able to recognise tone, texture, motion, focus. This means that color blind people often remain unaware they have a problem for years.