eBay, as ever, is your friend:
Orange Hairspray Fancy Dress, Fun, Halloween Temporary Hair ColourAlternatively, from a slightly more reputable source, but also more expensive, and not a spray:
Color Bug Orange... and there's also stuff like this:
Crazy Color Orangebut that's
semi-permanent, which from their blurb "can last aprox 4-8 washes".
I used some blue spray in my hair some years back for fancy dress. I've got moderately dark brown hair, and blue worked fine, but I'd imagine for lighter colours it may have less of an impact, experimentation is probably required! Do
not use your best white towels, some of the colouring will almost certainly not be washed out (unless you're incredibly careful), in which case the towel may gain various degrees of colouration. I've still got a towel with some large dark brown patches from ex-wife's hair dying, although that was a permanent dye.