Why wouldn't it be, the fact that skins should look exactly like the ref isn't pure interest for me, I want to get close, but still make them look good to my eyes, and a black mouth didn't do that. Also, the black isn't a mouth but more of a shadow, which isn't a need to put on a skin that doesn't have that many layers.

Star Fox

I had this thing in mind for ages. You just posted yours before i had time to finsih mine completely