I always play large or huge with occasional habitable planets and I don't recall ever having seen a purple star, for what that's worth.

Those things look pink to me. I got two of them in my last DA Large/Loose Cluster/everything Abundant/random minors game. Although one of those stars did not have a planet above PQ 7! What a major letdown... It had a 7, a 4, and a 3 that became something like a 12 after terraforming. At least I got the other star's PQ 26.

Playing DL, I once had a pink star that had two giant planets in a Small galaxy! One of those was the steroid variety, too, that goes up to about 56 after terraforming; I suspect those are mistakes in the code, but I'll take them every time.

I've had them in Medium and Huge galaxies too, I'm fairly sure, but I've had plenty of games with none, as well.

The star colors you get are a lot more varied if you play on lower planet settings--if you play on abundant all you'll generally see almost all yellows.

the purple/pink stars (I guess it depends on the monitor, I always see the purple stars as a deep violet color) are suppoused to be VERY rare, and always have been in the game. Its entirely possible to go several games without seeing one, even on a huge map.

I have seen them occasionally, although I don't know the ratio of the rarity.