Our Arabian mare Spin is nearly 30 and retired, so she is no longer ridden, but we still have fun pony party days where we use non toxic food coloring (found in the cake mix aisle at the supermarket) to color her white fur into all sorts of fantastic outrageous colors.
She doesn't mind in the slightest, and at the first hint of rain it washes out. It just goes to show that you don't have to ride a horse to have fun with it!
Sarah Herbert
Bomaderry
Australia