It's possible that most satellites are similar in color, but an additional likely reason for this is for the following physiological fact. The eye has rod cells and cone cells. The rod cells see only black and white, and are extremely sensitive. The cone cells see color, and are much less sensitive. When you look at something that isn't very bright, the result is that you can't see it in color. This is why you can't see color clearly at night when the light is dim. Most satellites are not that bright, comparable to maybe a 3rd magnitude star I would guess. That isn't enough light to see color very clearly.
You can see this effect very clearly when you look at a long-exposure photograph of the night sky, or when you look at stars through a telescope with a large aperture. The colors of the stars are much clearer than with the naked eye.