I've asked the Admins about it, and they said there is a limitation in the game executable so this could be the reason why you are not able to change the color for now, please use a different hairstyle.
Mohican is the only charming hairstyle where you can change the color from so i advice you to use a different hairstyle or just Mohican or stick with black color only.
they will disable the coloring in the next update, and until then once they found a way to make it able to color we will implement it.
Sorry for the inconvenience,
Happy Gaming.