I think this thread was maybe about REALLY REALLY purple bettas. From what I read, a blu-ish purpl-ish betta doesn't count, a slightly lavender-ish betta doesn't count, etc. I do see "Salamander" bettas on Aquabid a LOT. I think my Cornelius is a reject from someone trying to breed salamanders. (That's just my theory .. . I try to think about what kind of spawns my bettas from pet stores were rejected from . .
From what I read on this site, truly orange is rare. I have an orange betta but I am sure that is not what they meant. Reddish-orange, not rare. Really orange .. . . rare. I read that VERY green is rare. Not Petco green though. Petco green is probably a bluish green. Yellow is supposed to be rare .. but I doubt my Limoncello is rare . . because he is not 100% yellow, his gills are kind of flesh-colored, he has a few tiny black spots .. . oh yeah . . and I got him from PETCO (biggest clue). Also .. there were 2 others just like him and no one wanted them, it seemed. His "brother" is still there and I have had Limoncello for many months now.
I think rarity is in the finer details. It's not "is that betta purple" but what kind of purple, probably.