A super is generally the homozygous form of a co-dominant morph. NERD has a good page explaining how genetics work, but I can't remember the link right now and I always have trouble finding ANYTHING on their site. I'm sure someone will pop in with it though.

The 'ghost' that you're talking about is a recessive gene called hypomelanistic. It's basically a reduction of the dark pigment. It makes just about everything look better in my opinion.