A600/A1200 composite output is in colour, but as you said the A500's is in B/W which is always annoying when I can't locate one of my modulators.
Have you tried some of the CD32 compilation CDs that many people have created? Some contain over 800 games and I expect many will run on the CDTV. Underground gamer have a lot of them available for download if you are interested. PM me if you need further details, or an invite to that site.