One way for subtle colors; just stack a few surface layers, give each a nice earthy color, mask them each by a power fractal, and set their coverage to 50% or thereabouts. That will mingle into a nice blend of clors of your choosing. For even more variation add another PF to the color input so each basic color will have a 'lightness' range between the colors of the PF (white--black, or lightgray--darkgrey). Many possibilities, you can even distribute certain colors by slope, or height. You can add this stack of colors as a child of a main surface layer in the line to planet.