> I don't think a food grade powder that will wash away with the next rain counts

Your evidence for it "washing away with the next rain" would be?

Ever see what a child can do with a glass of "cherry" Koolaid?

A dye being labeled as "food grade" has essentially no correlation with its permanence.

> Does sidewalk chalk count as vandalism?

Sidewalks aren't 4,500 year old World Heritage Sites.