What has been said above is just about it. But directed towards the plaid junkies. If you are wearing a solid grey pair of pants, moving through the timber, with a plaid top, that is still a big chunk of grey that the deer will see.
Think of it this way, try moving a peice of grey paper behind a screen. You can definatly tell the paper from the screen right? Now move a peice of screen behind the screen, what do you see? Just screen, so if you wear something that looks like a treebranch, and you move slowly, and stop now and then. Chances are they will think you are a treebranch. Anyway that is just how I look at it. Then come gun season I have to stick that bright orange hat on my head. I am still not bought on this "deer see shades of grey bull", that is just something someone made up back in the day to get hunters to wear orange, lol