Most of the mcpony g4s have sculpted manes and hair tails. However, (correct me if I am wrong) the pony is made of one solid piece of plastic. It is not jointed even at the neck. So changing the hair would require cutting and sculpting. Have you considered dying the hair instead?
Also matching paint to hair... paint tends to dry darker than it shows when wet so I would do color samples to compare to your hair colors for a match.