I painted a 1/6 scale garage kit once and chose the following colours:

Basically, it is dark grey with highlights of VGC Dead Flesh('Rotting Flesh' if You use EE colours). Sorry for the large pic, but with such a large scale, small pics would be a waste...
I hope that it helped.

A more realistic approach such as the one in the Frankenstein film with Robert de Niro as the creature would be interesting as well, IMHO. It would be very hard to prevent them looking like zombies if You would try it that way, though.