I got the Sketching set and I was thinking of maybe getting the fly-tying set as well which should give me a broadish range of colours.
I've seen an online demo somewhere (I forget where
) for promarkers/copics and they were using an eraser pen to add highlights to coloured in images and make effects like scales etc. Do you have or can you get anthing like? I'll see if I can find the link to the demo if it helps.
Found it:
http://www.splitcoaststampers.com/resources/tutorials/texturewithalcoholmarkers