I'm glad my spectre was in attendance Malone. As soon as I read the preamble and saw the reference to shading I knew I was in for a treat.
I've been busy today so have had put it aside until Monday. This works out well as a work such as this deserves a new set of colouring pens, which I can pick up from the craft shop tomorrow.
No doubt I'll be back here periodically looking for help, the switching of some definitions sounds particularly tricky.