If you're looking for different skin tones, and then using Photoshop to make specific characters, why not just use Photoshop on the basic M3 textures and use layers to create the skin tones you want first, then flatten and modify to create specific characters? As long as you're not redistributing, you can do anything you want to textures - I made my Andorian texture by layering the right shade of blue over the standard SP3 textures and then changing the blend mode and transparency to get exactly what I wanted. It works like a charm.