I think the surfacing is fine. At any rate if you look at real rocks any way you will observe that they have a base color and between three to four other colors and that the over all appearance or the rock is quite even and in cases (Rock type dependent) looks quite bland. In any case (Sorry to those who know this already) what you are seeing are different minerals and their distribution through out the rock, hence the colors. If you look at slate for example there is no variation in color the same gose for other rock types to.
Yes, there are rocks with a great deal of variation in color but these are not representative of what is commonly found, if other people in this community have made different observations that is fine, I can only state what I my self have seen.
Regards to you.
Cyber-Angel