How I paint - Eyes/Nose/mouth - Grayscale to color

Beware !!! Huge canvas !!! This was a desperate attempt to stay awake ... not working, GoodNight XD

Explanation : I USE THE DEFAULT TOOLS OF PAINT TOOL SAI !!!

Step 1 : Line/ clean sketch - SEPARATED LAYERS
2 : On base layer, add 1 shadow.
3 : Merge layers and blend shadow/base color. ( watercolor tool )
4 : Add 2nd Shadow ( airbrush )
5 : details and refine the eyes.
6 : IF YOU STOP AT THE GRAYSCALE : Add highlights.
6-2 : IF YOU ADD COLORS : NO HIGHLIGHTS ! Red ONLY on overlay layer 50%
7 : Add Colors : Skin, eyes on multiply
8 : Redness, eyes on overlay.
9 : Luminosity layer : highlights.

Last thing : NEVER use black and white on a grayscale if you're gonna add colors !!!

That's how I work on grayscale and grayscale to colors. It's a technique I've developped from experimenting myself so there might be better way of doing it.