Purple trichome heads are a rare sight, which I've seen in maybe 1-2% of plants that I photograph. It is so rare because even when I have seen that strain produce them in the past, often certain individual plants will be the only ones actually displaying it -- it depends largely upon the plant's maturity, as the purple heads generally seem to fade with time. The purple pigment in the heads (and the rest of the plant for that matter) is anthocyanin; what is less clear is why exactly the pigment seeps into the trichome heads rather than stopping at the stalk (which is a much more common sight). Haven't shared these in a while and have gotten a lot of new followers since then. So, enjoy!