Hi :) it took me a while to figure out how to blend and achieve a smooth non grey color in SAI. Got more into this technique thanks to Sara Tepes, on youtube ! The basic trick is to make 2 layers, one on top and one underneath the b&w layer, top and b&w set ot overlay and fill top and bottom layers with starting undertones... Mess around with the colors until you feel ok merging the three and start adding more tones for dimension.