Blow up a bomb on screen 80, and exit back to the overworld.
Screen 80's palette has now copied itself over to the overworld. 😮dd:
Amusingly, the reverse happens if you buy the large triforce in a screen 80 shop: the cave gets the overworld palette. 😛
I can confirm the first part of this (the part with the bomb). Interestingly, my colors normalized when I entered a "dark room". It's still pretty strange though, and it's certainly not good.
Specifically, this bug occurs if the "Bombs don't flicker palette" rule is disabled.
Fixed in the next build.