I used the head without a helmet from the Prince and Noble set. Looks cool. I'd definately make him a prince though, Dragon Mages are fun, but squishy squishy squishy!
Colours? Hmmm, the rider should tie in with your army scheme but the dragon doesnt have to, so you can go for whatever colour really. Mines a light bluey greyey white, with purple scales.
If you want to get rid of any of your spare High ELf bits, chances are I'd want them. Im after all sorts at the moment as Im completely converting a new Elf style army.PM me if so.