Considering how many years silver, white, red and black GPs have been produced for instance, the amount of factory purple ones is considerably less. A color alone may not make a car "rare" but one equipped like mine makes it even more so. I doubt there are to many that view Cudas and Challengers from the 70s in the color "Plum Crazy" as sissy, gay or "chick cars".
Even Pontiac came out with a different, even nicer ( i.m.o.) purple metallic color for the 1998 Trans Am ( and possibly all Firebirds). I wanted to order a Formula in that color but I was told that due to little interest , that color option was cancelled early on in that year. Finding one now, would indeed be a "rare" find. The latest generation of GTOs from '04-'06 had a purple metallic '04 available. Only one year offered. First year for the Chrysler Prowler was available in dark purple metallic.