If they have like a like of brown down a black nose, I have heard that was due from their nose rubbing against a plastic feeding dish.
TJ has a full complete dark brown nose, which I think might be the sun related thing, or he has a full brown nose
Roxy had a black nose and I used to feed them with plastic dishes, and that's where she got her 'brown stripe' - no matter what, it won't go away.
They both eat from glass dishes now.