I’m not a plant person but I do make my own dyes and pigments from organics. One of the ingredients I use to precipitate the pigment, or as a mordant, which can change the colour, is aluminum sulphate - also used as plant fertilizer to raise soil acidity.

The chemicals that produce colour in plants are super sensitive to PH, there’s a plant based paint company, I think in Europe somewhere, that makes everything from green to red to blue out of just red cabbage.

I don’t know if that’s what’s happening here, but it is indeed super neat.