As this model is destined for rendering, it's going to need a lot more accompanying maps than simply a texture map. Along with the texture ( or colour, or diffuse, whatever you want to call it ), you will need a bump map, a specularity map, perhaps a translucency map. This can be taken a lot further to include all sorts of other maps, but for the Moff Tarkin image, I got away with just these. So, the tricky part, is working in a fashion that enables you to keep a relationship across all the maps. This is why all my maps I keep stored in the same layered .PSD. If you end up working this way though, be aware that this PSD can get huge in file size ( Moff Tarkins face PSD is over 100 megabytes ) , since you'll end up with many many layers and need a resolution of at least 2048 pixels square. Get that ram you've been saving up for. I have 1.5 gig and could still use more.
Tip: get a wacom tablet! :)
So, in Photoshop I've created a .PSD with the exported baked shader as a layer, along with the UV layout as a layer. I've then sized it to about 2500 pixels square. ( uprezzing images is generally frowned upon but Im only using these as templates ) This resolution is perhaps a little overkill, but I wanted to be safe not sorry. I think for most uses 2048 is fine. For painting the colour map, I've blatantly stolen some concepts from professional sculptor Vance Hartwell. Check out his site here, as he has an awesome tutorial on how to build up the different layers that are needed to achieve convincing human skin. Using this principle, and examining images of Peter Cushing, this is how I built up the layers for the skin colour map:
1. Subtle stipple for skin pores ( very subtle, you might need to zoom in to see it )
2. A reddish mottle, vaguely meant to represent blood flowing under the skin
3. A red that's meant to represent discolouration of the outer layer of the skin. Mainly sun damage. ( If painting sun damage think about where it would be most obvious. Generally the planes of the face that point skyward ) I have erased into the sun damage on the cheek to look like wrinkles.
4. Purplish tone for bags under eyes
5. Beard stubble
6. Moles
7. Veins
8. Random blotches
9. Eyebrow hair ( For a more realistic look however, I would recommend treating hair differently than painting on. See later in the tutorial )
10. Age spots
More 3D Graphics: 
