Have you ever seen this?  I took her to the vet and they said to just watch it and were not concerned.  It is not raised, not crusty, still has little hairs on it, it has just lost its pigmentation.  That side of the lip looks the same as the other, just lacking color.  She does run her nose smelling where animals have been, i.e. the oak tree, pecan tree, fence, etc.  I don't recall it ever being red, but perhaps.  Do you think it is just a scar now?

I've re-posted the picture for you.

Bo has something similar on his snout, but not as big. It's like the velvet has been rubbed off, but not sore or red. he also has what looks like a little white, slightly-raised lump on his lip that has never changed -- again, not red, not sore. I'm with the watch and wait school.