Is there no way to use colored squares mode in IntyBASIC? I don't think I've ever tried it.
Oh wait, is it just color stack mode, and you set bit 12 on a card? Does that mean you can mix and match the modes?
Yes, just set color stack mode, set bit 12 and clear bit 11 in card. This means also you don't have access to GROM cards with "high" colors.