Well on this I would say that the curse would null it out and then the dye 
would be
 
gone when he changed back. My reasoning for this is I think the curse used 
Ranma's
 
original DNA as a template for the female body and created a new body, 
however it
 
has to recreate his old body again when he is splashed with the warm water.
Therefore his bodies are constantly being recreated every time he is splashed 
with
 
warm or cold water. That at least is my theory on it since Takahashi Sensi 
never
 
discussed the mechanics behind the magic of the springs.

Sven L33TM45T3R wrote:

>      what about What would happen if ranma were to dye his hair while a girl?
>   would it stay the same when he transformed, be darker becouse his hair is
> naturally black as a boy or would the curse void the dye and make it black
> again.....and if the third is true would it return when he changed again or
> would it be red once more?
>
>
> Desperatly trying to restart that rush of letters we had going       awhile
> ago and re-spark all our obsession with the Ranma phenomenon.
>
>
>   GORBASH The L33T Otaku.
> --