I used the colored hair spray on my pony. I cut out a stencil and just sprayed it on. It ended up being very powdery, and just wiped off. Good for temporary stuff, but probably not the best thing to have around kids-- I don't know how well it comes off clothes. But I think it would be fine to put streaks in the mane and tail without drying out too much. Horse hair isn't quite the same as people hair.
I've also read that you can just use non toxic poster paint, or children's finger paints for that. Most of them come out pretty easy with just normal bathing, but be careful of dark paint on light horses, like black on a white horse.
Impressive Wild Angel- Ginger Happy Go Lucky- Duncan Little Boy Blue- MellowSweetwaters Eqyptian King- Sam