Like Celcia already said, chalk can be messy, especially in the unpredictable conditions of a convention. Honestly, if he's really wanting his hair to match, he needs to dye it using real dye or suck it up and wear a wig. As long as you get good one, they're really not that bad. You just have to get over the initial "wtf is this thing itching at my scalp!" phase.
'Idiot's Lantern' Rose Tyler (Doctor Who)
Astrid (How to Train Your Dragon)
Tinkerbell (Peter Pan)
Reviving This Year:
Annabeth Chase (Percy Jackson)
Katniss Everdeen (Hunger Games)