I just checked and here are the specific botanical definitions:
Pistil = Entire female part of flower (aka "gynoecium") . In the case of cannabis, the pistil includes both the stigma AND calyx (see below).
Stigma = pollen-receptive part of pistil. In the case of cannabis plants, this is the "hair" that people talk about, that changes color usually to orange or brown late in flowering. By convention, most people in the cannabis community incorrectly refer to the stigma as "pistil", and I've been guilty of this myself.
Calyx = outermost leafy part of female flower. This is the "good" part that's covered with trichromes.
You can click on this link for a picture of a plant with pink hairs (stamens):
http://www.420magazine.com/gallery/data/500/10-8-09_015.jpg
I've never seen a cannabis plant with a true pink calyx though I'm not saying they don't exist.
On the other hand, some of the "purple" strains can make a bright light purple that could be considered pink, depending on lighting, and what you're willing to call pink, and I've seen plenty like that:
http://forum.grasscity.com/photopost/data/500/medium/IMG_2384a.jpg