In response to this question about iconography, I was wondering about how much it is necessary to factor in color usability for people with color perception difficulties into a design.
The first instinct is to say of course it's very important, but note that I don't mean the question as 'How much do we have to bother about colour?'.
What I'm wondering is whether people with color blindness are so used to dealing with colors around them in their everyday lives, that they barely even have to think about interpreting the colors - provided there are other indicators to assess the differences.
For example - a typical scale or range of colours is red/amber/green - used internationally for traffic lights, progress indicators, status lights etc - in software and hardware.
Is it necessary to re-assign these colors so as to cater for every type of color blindness - (is it even possible), or are people with color blindness quite used to dealing with (or working around) these colors, making it unnecessary to actually change the colors away from these standards.
So - in addition to secondary (or even tertiary) indicators such as symbol, shape, size, position, number and labels, how important is it to consider the actual color for color blindness in a design.