Seem to not be consistent but it happened to me recently playing as Ob against a Kiora and several gems were converted to green and another time pre 2.1.2. I can’t recall the PW i had but i remember it converted to a red gem and I was not using a red PW.
@Brigby I’m bumping this post. Can confirm that this bug is in game.
Before gem change (note that there is a white gem in the second gem down, second from the left position), the gem is white. I’m playing Ob Nix with Painted Bluffs and no other gem changers, so it should turn black.
I just had this happen in training grounds against Koth. He was the one who used painted bluffs, but it was turning gems purple. Super nice for me as Liliana3, but not the way it should work.