Definition - What does purple cannabis mean?
Purple cannabis is all cannabis flowers with a purple hue or tinge. The purple exhibited by purple varieties of cannabis is not always a deep purple like one would expect, and can sometimes vary from a dark green to bluish to even black. The same compound makes blueberries blue and purple buds purple. This compound is called an anthocyanin.
MaximumYield explains purple cannabis
Anthocyanins are water soluble pigments found in many plants, and depending on pH, their phenotypic expression can vary anywhere from purple to red to dark blue or black. Anthocyanins are a type of flavonoids, coming from the Greek word flavus, meaning yellow. In order to make a cannabis plant turn purple, anthocyanins and other flavonoids must be available in soil. To accomplish this, the pH must be either neutral or slightly acidic, as more alkaline soil makes anthocyanins unavailable to plants.