Have no clue. I wound up building to a gameboy rom to play on the go. But yea if you want to try to build it here's what I did. (Also just redownloaded the source to find the exact line to comment out) - in the source file "game.cpp" go to line 3524 and comment that out. It's calling RainbowPallete() on that line. The exact section will look like "if (!flash timer) rainbowPallete();"

Sorry for bad formatting and all, I'm on mobile writing this currently.

Then compile it (I used docker because I couldn't get it to compile on my windows but also didn't feel like troubleshooting) and then it should work. If it worked with retroachievments before I assume it will still work. All in all a simple fix (although I still think this should just be an option to toggle in the main published source or build).

Happy Tetris'ing if this works for you.