The method I use is to create an alpha map of the brows and use a hue/saturation layer in photoshop to tint the brows. You can also use this alpha map in the material room of poser. My advice would be to pick up the V4 brow overlay from Netherworks (should still be available for free at Content Paradise and in the DAZ freepozitory). It comes with a tutorial on how to use the overlay. Take a look at the alpha map of the brows and the way it is attached in the material room nodes. This should get you started on creating your own overlays for different textures.