Getting Rid of Weeds in Rocks?
The blue stuff landscapers use is this dye: https://www.amazon.com/Liquid-Harvest-Concentrated-Pattern-Indicator/dp/B01G7M309M/ref=sr_1_4?tag=thrif06-20 You just add a bit to whatever youre spraying. It doesnt last long in the sun - I spray it between flagstones...
