fortunately, because of this, all images of this type that I make I choose red, yellow, and blue normally, before I start using secondary colors...

Interesting. If I went over there and found a map that was using yellow against a white background, I'd probably be bitching about that, visibility-wise. I wonder if there is a style guide for color-related stuff. My friend actually specializes in adaptive technology, but he's out of town; I'll have to ask him.