This has nothing to do with color palettes, I already had this problem before, but I solved it choosing the option clicking rigth on toon boom and choosing: “run with graphics processor” option, and it worked fine for a couple of weeks
but suddenly the problem came back and this time it seems that I cannot fix it.
You may need a better graphic card since it sounds like you may be using a laptop. Remember that laptop systems don’t usually come with a goods graphic card. Make sure that you are not running on battery power since the system will default to the onboard card to save power if you do have a decent graphic card installed. Also try updating the graphic driver of the card which may help.