A) I'm not brave enough
B) I have a customer facing job!
So I decided to experiment with chalks or more precisely soft pastels, you can buy chalk that is especially made for hair but it is more expensive, I used soft pastels from an art shop to create my rainbow hair! My hair is very light so I didn't need to use water to get a good colour payoff, I literally just brushed the pastel on, but you can spritz your hair with water first if you have darker hair and want the colour to last longer. You can also use straighteners/ tongs to seal the colour in when finishing. Mine washed out after 2 washes, obviously if you use water first the colour will last longer.
Before you start make sure your soft pastels are NON TOXIC and DO NOT breathe in the dust! You will need gloves and old clothes you don't mind getting dirty when chalking, the colour may transfer onto clothing and bedding so wear darker colours. Don't use oil pastels they will make your hair a horrible sticky mess!! Make sure your hair is product free.
I love my rainbow hair !