Sophie,

I've used temporary haircolor contained in spray cans (like the ones they sell for Halloween) and spray it on a disposable mascara wand. And I've also used the temporary touch-up haircolor packaged in mascara-type tubes found at public beauty supply stores like Sally's.

FYI - I wouldn't use it if the model will be sweating or water may interfere because the product may run into the eye.

Good luck!
Mary Anne Mendes
Makeup and Hair Artistry
www.makeupandhairartistry.com
www.myspace.com/makeuphairtist