Which makes a perfectly good reason to do it.

“Will, what did you do in school today?”

(bending down to show me the streaks of red, blue, and yellow) “Painted my hair.”

“I see. Did anyone else paint their hair?”

“No. ‘Cause the teacher said it wouldn’t wash off.”

(Parental note: Dip in the neighbors pool, followed by a good washing in the shower, got most of it out.)