Many good reasons have been stated for wool. For thousands of years it has been the fiber of choice for cold, damp conditions. Our winters in Georgia are usually mild, so I don't need the really heavy parkas and bibs (although I do use them sometimes). Medium weight is just right.
My preference is a muted plaid that has a somewhat light background. My son, an art major, has really helped me better understand the use of background color. Light, but not stark, backgrounds tend to give an effect of emptiness as opposed to looking like a solid object. It tends to make one disappear. Some wise old deer will bust you anyway, but I thinks it is a valid concept. In the winter woods, grey is more or less invisible.
Combining wool's camo effect and its quietness, I believe it is a superior fabric for hunting. True, I still use a lot of modern fabrics, particularly military camo with success, but they just don't mix well with dampness as effectively as wool. To me, nothing short of design specific raingear will handle a real downpour, but since I no longer hunt in severe weather, wool works well.