The difference between the blue and purple color of black goji berries in water is mainly related to the pH of the water and other factors.
The color of black goji berries after soaking in water is mainly related to the anthocyanins in black goji berries. Anthocyanin is a natural pigment in plants, soluble in water, black goji berries are more abundant. Anthocyanins in different PH (pH) solution shows different colors, anthocyanins in alkaline solution is blue, in acidic solution is red, and in neutral solution is purple.
Therefore, anthocyanin-rich black goji berries will show different colors according to the pH of the water, i.e. blue in alkaline PH water and purple in acidic PH.