everything said here pretty much rings true... I get asked all the time what a mapmaker can do to make their colors colorblind-friendly, and since there's no single type of colorblindness there isn't much I can say.
The trouble usually isn't with the larger fields of a single color. For instance, on Tack's Citadel map I can easily tell the regions apart. Regions can become problematic when the colors have some marbling going on, as in the Texas map - within any one region there are several shades, some of which resemble shades in other regions. Some maps are more trouble for me personally, because they use colors next to each other that I have particular trouble with... one example being the blues and purples in Battle of Actium, which I avoid.
The bigger problem is with small samples of a color, such as thin lines or text. For instance, I can't tell some of the army count colors apart - the red from the green, the "c" from the "p" whatever they're supposed to be - but the colorblind game option helps overcome this. (Mapmakers should be aware that when using the colorblind help, all two-digit counts become three digits, so leave plenty of space around your army circles!) What the colorblind help does not assist with is any features of the map that rely on my being able to determine a thin area of a color, e.g. the name of regions in the legend of the old Citadel drafts, the legend boxes in Indochina or circles on Ireland, the color of the borders in the Dark Age Britain drafts, or the color of a rail line or station in Rail USA.
How to make your map colorblind friendly:
1. Use texture or patterns as well as or instead of color. The new France map has a nice the textured border glow.
2. Use inset maps - can't go wrong there, because even if I can't tell the colors apart I can use location as my guide.
3. Give some other clues on the map itself - location or text clues - as cairnswk has been good enough to do in the Rail Europe map.
I'll try to think of more, but right now I'm late for work!