Dye your hair with color pastels.
I saw a nice tutorial here > ♥ so I try it out, and the end result was great :o)
It is so easy to apply, I use the pastels of VanGogh, these are great!
Don't use a oil base because Removing oil pastels would be a nightmare, not to mention, they'd feel very sticky.
After 1 or 2 washes it's all out again, not pernament, but super fun to do :) Conditioning treatment is a MUST after you wash out your chalk.
You can also paint your hair with food coloring, but I should try it another time!