I've never seen this in a BP, so I truly HOPE it's genetic, but other than staining from substrate, my brain leans over to septicemia or burns...really hoping it's neither.
It's a little quieter on this forum lately, ppl have a lot on their minds (like eating & paying bills, maybe) but it worries me that among all our knowledgeable members
-many of whom breed BPs- no one has seen this phenomenon before. I'm not saying it couldn't be something genetic, but...I'd keep all options open if I were you.
(Ask yourself WHY if it's so pretty & something rare was it "turned in to a pet shop"? Maybe a vet suggested expensive treatments & the owner decided to bail out...)
I'm not trying to ruin your day...I HOPE I'm wrong & you just came home with a million-dollar genetic anomaly, but think about the odds...
How long have you had this snake? Is she eating? Behavior normal? If she's not your only snake, I hope she is quarantined! Stool ok?