Sketching the concept!
I always sketch on light blue!
step 2 of 4
REALLY quick colors, just to check out lighting, etc, deciding where light source comes from.
step 3 of 4
Using pen tool and vector masks to cover up the quick brush strokes to give it a more defined shape.
step 4 of 4
Blending all the colors on a new layer.
Sorry I got carried away and forgot the SBS :/
Used a semi-transparent brush and kept on using the eye-dropper.