My previous Betta (Quimby) changed colors as well. But he was pink with a bright blue tail, and then changed to a more salmon color with a red tail. I thought it was 'magic' too, until I noticed one of my earrings fell into the bowl. Woops! Haha. I don't know if that had anything to do with it...
Signed up so I can get some answers on this problem. :/
Anyways, I have a cycled 20 gal tank. It's been running since December (we've already gone through the deaths and drama of fish during the cycling) and all the levels are good now. I do 25% water changes (and vacuum the gravel) every week...