Purple is an exotic color in the cannabis world. Connoisseurs salivate over varieties that are saturated with rich, violet tones.
What gives cannabis its purple color? Plants are sculpted by the interplay between their genetics and their environment. There are many cultivars which are normally green or gold but will produce purple or pinkish hues under the right conditions.
Purple cannabis gets its color from anthocyanins, a type of flavonoid that gives rise to purple, red, and blue tinges in flowers and plants.  These pigments are present in every part of the plant, although not necessarily in concentrations high enough to produce visible coloration.
Cannabis varieties that are rich with anthocyanins aren’t always purple. Their color depends on the level of pH. Anthocyanins appear reddish in acidic environments and purplish in neutral ones. At higher pH, they lose their molecular integrity and break apart, causing no coloration at all. 
Most plantsproduce anthocyanins. They’re responsible for the color change of leaves. However, the plant’s appearance might not be altered until it enters its final flowering stage.  Pigments in the plant often appear brighter when they don’t have to compete with chlorophyll.
Research indicates that anthocyanin degradation is significant at temperatures over 75°F.  Therefore, it’s vitally important to keep purple cannabis varieties at room temperature. This is especially true after they have been harvested, as anthocyanin concentrations are mostly maintained in vivo by a dynamic expression and degradation process. 
Making purple extracts can be a somewhat difficult process, because of the temperature and pH restrictions. One way to work around that is with a rosin press, a solvent-less extraction process. The flower is compressed under heated plates before the cannabis fully dries. The vaporization of water protects the molecular integrity of the THC and anthocyanins from overheating.
Phil Salazar, inventor of the rosin process, has some advice.“A good range to press flowers is 200-230°F for 10-30 seconds, depending on variables like stability and terpene loss.”
- Khoo, HE, et al. “Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits”, Food & Nutrition Research, 2017, Volume 61.
- Laleh, GH, et al. “The Effect of Light, Temperature, pH and Species on Stability of AnthocyaninPigments in Four Berberis Species”, Pakistan Journal of Nutrition, 2006, Volume 5.
- Niu, J., et al. “Anthocyanin concentration depends on the counterbalance between its synthesis and degradation in plum fruit at high temperature”, Scientific Reports, Volume 7.