Purple is always a gamble (whether it comes out or not), every pheno is different. Here's two grandaddy purples, seeds both from the same plant. One went purple, one showed more of the Kush heritage.
It is called just that "The Purps" . If you google it you will see that it is more frequently green than purple.
Its a crapshoot. I have some triple purple rhino tucked away, supposedly those are more likely purple than green.