Thanks very much guys.
These are largely just studies for getting the structure of the nose right, I haven't really touched on any colour or light theory yet so I'm just having fun with it to keep my practice interesting. For the shading I was just trying to get something in the region of the references, though I was generally sticking with my own colour choices for them.
I did throw a couple of reds, greens and blues into the shadows but I think maybe they are too low opacity to be noticed! I'll push them a bit harder next time.