Loading the methodology
Purple color is genetic expression, not quality signal. What anthocyanin levels actually indicate about the plant's biochemistry.
Purple color has become a quality signal in the consumer market. It shouldn't be. Anthocyanin expression is primarily a genetic trait, triggered by environmental conditions rather than indicating anything inherent about quality or potency.
A genetics without significant anthocyanin coding will never go purple regardless of growing conditions. A genetics with that coding will express color whenever the right conditions are present — typically cooler temperatures in late flower and adequate pH for anthocyanin stability.
In a living soil environment where secondary metabolite production is supported by root-zone biology, anthocyanin expression in compatible genetics tends to be more complete and stable through cure than in synthetically-fed equivalents.