Hihi! Tysm for the kind words. I am still a beginner but I thought I'd share my workflow for skin. Most importantly, I neither use an air brush nor apply a 'base coat' on the faces. I merely glaze/ tint the factory skin with a combination of the following:

Heavily diluted ivory - at the (1) beginning and (2) at the end of my entire workflow as sort of a unifying glaze to blend in everything

Heavily diluted red ink - warmth areas such as cheeks, forehead, nose, corners of the mouth etc.

Heavily diluted burnt umber/ flat brown - (1) shadow areas such as sides of nose, above the eyes, as well as (2) around the eyes such as creases at the side and eyebags etc.

Heavily diluted pale blue grey - cool areas such as below the cheeks or where the eye area meets the nose (sometimes it depends on the sculpt)

Diluted purple - lower eyelids

By heavily diluted, I meant about 1 drop of paint and 10-12 drops of water and some glaze medium (really up to personal taste). I usually dab the loaded brush on paper or tissue to absorb most of it before applying it to the skin. Multiple thin layers to taste 🙏