I've experienced something similar once before, but mine was more drastic. It was at least 2-3 years ago and I still haven't figured out what it was caused by. The snake was a pet store buy in like 2000, nice looking normal. Well around 2007 a random white spot showed up and covered about a 1 cm area. I posted pics on a forum and never got any real reasons. I know burns can cause white but his was definitely no burn, the scales were white. The area crossed over his black pattern and brown parts. A few sheds later the white disappeared and filled in black. It is kind of odd because it overlaps where it should be brown, not black. This guy has HUGE pied markers as well, I doubt they are related but figured I'd include that

I know it doesn't help, but I figured I'd share my story Well heck I just found a pic of the white spot, and it has a date on it! I also just took a pic of the spot now so you can see. The white spot was more dramatic before it went away.