For the article about genetics, I did a while ago. I searched for existing morphs. I must say that I only searched for mentionings in sites, not official papers of the like. I found that these should exists for marcianus:
-melanistic
-anerythristic
-snow
I've not seen them available, although they are mentioned to be available sometimes...
I've not found many pics either, but 1 site had this one:
Altough, in my eyes, you can't say much from the pic...