Chauncey... I can't draw a lick so it is amazing to me THAT he did it. But obviously, he used a Wacom, pencil brushes of various size and opacity to draw the shapes and soft shadows. Then he built up the drawn detail.
As for colorizing, I saw the color picker flash by as well has Hue Saturation dialgos. I think I also detected color overlays.
But it still takes someone who can DRAW. And someone who can draw AND has a basic understanding of
PS should be able to figure it all out.