The utility of various hues depends entirely upon the situation. I have spent countless hours searching for lost/departed souls dressed in dull, earth tone colors. While bright colors do make you an easy target, that is a good thing, especially if you are in any kind of distress.

I was packing for a field trip the other day, throwing in mostly normal, fairly dull colors, and then I added a bright orange shirt, thinking "you never know, this just might be handy...."

I think this "gray (or is it grey?)man stuff is pretty conjectural. I doubt that the bad guys pay much attention to the color, or even the colour, of your garb.