In general, spray paints are not intended to be applied to the body or hair. Spray paints, especially those containing organic solvents, may cause allergic reactions or other irritation. Eye contact is especially dangerous. As for the spray paint on the hair, it all depends on what kind of paint is in the spray can. If it is a water-based chalk wash-off paint, it can be washed off the hair with water. If it is alkyd or acrylic paint, it is impossible to wash it off without harm to the hair and scalp - you will have to cut your hair to zero.
Depends on the type of paint. Acrylic is relatively easy to wash off with warm water and soap or shampoo (the first is better), in the case of automotive nitro paint it is easier to shave baldly. More precisely, this will be your only option :)
I think this will be your last coloring))) at least with this hair) the paint will dry out and the result will be much more resistant than from the usual paint)