Like other purple basils, the purple color is from anthocyanins, especially cyanidin-3-( di-p-coumarylglucoside )-5-glucoside but also other cyanidin based and peonidin based compounds .'Dark opal', along with other large leaved purple cultivars such as'Purple Ruffles', has a high concentration of anthocyanins and is considered a potential source of red pigments for the food industry.
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When the pH is changed, the extent of the conjugation ( of the double bonds ) is altered, which alters the wavelength of light energy absorbed by the molecule . ( Natural anthocyanidins are most stable in a very low pH environment; at pH 8.0, most become colorless . ) At pH 2.0, peonidin is cherry red; at 3.0 a strong yellowish pink; at 5.0 it is grape red-purple; and at 8.0 it becomes deep blue; unlike many anthocyanidins, however, it is stable at higher pH, and has been isolated as a blue colorant from the brilliant " Heavenly Blue " morning glory ( " Ipomoea tricolor Cav cv " ).
