Fallout appears to be running in compatibility mode. (see screenshot for full message since GOG forums won't allow the text for some reason)
Clicking 'OK' closes Fallout 2. I've tried the regedit trick where you remove the 256COLORS reg to no avail.
Unfortunately, this also means the next version of RP will not work since it ships with SFall 2.20. I am not aware if it is safe to downgrade SFall while using the soon-to-be-finished RP beta, but it would be great to have a heads up on the problem before it is officially released.
Thanks for any help!