Based on other purple basils, the color is from anthocyanins, especially cyanidin-3-(di-p-coumarylglucoside)-5-glucoside, but also other cyanidin-based and peonidin-based compounds.
The purple hue of basil stems from anthocyanins, specifically cyanidin-3-(di-p-coumarylglucoside)-5-glucoside, along with other cyanidin and peonidin derivatives.