I had forgotten about this until I grabbed her today and felt it again. Greg Graziani has an old you tube video where he shows a dark female he tried to as prove genetic (wasn’t) that had a small bump that literally just leaked melanin? It looked like the tip of a marker.
This Genetic Black Back (GBB) female developed a much smaller lump than Greg’s, right around 2.5-3 years old. It’s not perpetually open either. For a year or so I didn’t think anything of it, until she shed one time, and wrote on all the walls with a sharpie
I have no idea what causes it or what the long term effects might be but it doesn’t affect her in any obvious way. Makes cleaning her tub a pain when it opens but it’s only happened a few times. I can’t find any of the pictures from the last time it happened, if I do I’ll post them.