You could use the three first colors of Duessell's hair, though, that'll give you a slightly purple tint on the white.
Even if you made your own colors, the outline color REALLY contrasts against the hair. Also, there's no shading on the back of his hair.
And using the actual FE8 portraits as your defense to why your sprite is the way it is, isn't really that good of an idea. Most of them are pretty bad in the first place, so...
Really, just make the hair darker, and shade the back of the hair.