Anyone who has ever tried natural dyeing knows that we need a mordant to fix the colour.
Alum is very good and natural. Some use vinegar or iron or gall or other such.
I may be the only person in the world who can sit and watch this all the way through in awe.
I saw much the same in Karachi – from a car. The colours are amaze-balls :o)
P.S. I’m not 100% certain but the white powder he throws in could be alum.