A while back I watched one of  Horrorbuns streams and I really loved how he colored, basically you get your lines down then bucket the backround a color you want use the marker tool (on SAI) and darken shaded areas, then water to blend it, then marker again with a highlight color, then water to blend again.

Horror was drawing a bust of this guy and that's that made me do this! Definitely coloring like this from now on <3 and it only took me like 30 minutes to do this as well~