The hair color is determined in-game by the shader:
<shaders>
<shader><file>/planeshift/art/shaders/colorize.xml</file></shader>
</shaders>
...
<materials>
<material name="dermm_hair">
<texture>dermm_hair_texture</texture>
<shader type="standard">colorize</shader>
</material>
Unfortunately I don't know how to manipulate that in ViewMesh, so I end up removing those lines and just changing the color of the hair texture file itself.