It's probably making TG even more complicated, but you have a point, although it would be best to be able to choose your color. I would like to add that for objects like buildings it is often desirable to be able to see from the wireframe whether it's under ground level or above (to check if a structure is not floating at one point in an undulating landscape, for instance), so a part of the wireframe in another color. But that's probably hard to implement.
