Actually, it seems to be the other way around. I tested it with a previous game, which was 16-bit, and it worked fine. Switched to 32-bit, and it became transparent.
Started a new test game with 32-bit right off the bat, and it worked fine. I downgraded to 16-bit, and both the text and the bubble's background changed to weird colors. Back to 32 and back to working fine.
My current game was 16-bit, and I recently changed it to 32-bit. Maybe that's the problem. Downgraded to 16-bit to test it out, and it isn't transparent anymore, just weird colors like in the test game:

I'm not comfortable sharing my entire game files, I hope you understand.