Now a vein layer , your hardly even see these if at all, but it gives the impression of something under the skin. you could pick out one or two that looked the best and copy then on to another layer and make them stronger.

Then use the same vein layer on the bump map using colour dodge to make a slight bump where the vein is.

Here's the sort of finished colour map but you can't really say finished, things always need tweaking.

Now I can't provide this full photoshop file because its 400mb big. So i've had to reduce it in size and cut it down its now 684 by 1031 18mb in size.

The picture below is what's left, i've also had to compress it with the program winrar, because it's the best compression program, and I had to get it as small as possible, I have a slow connection and uploading takes for ever. If you can't use winrar sorry their's nothing else i can do.

Now before showing some of the other textures I use, I will show you one of my skin shaders and try and explain the connections, below is a map of the connection for my maya 4.0 shader. I have colour coded various parts, it's basically made up of five different layers.

I'll start with the Bottom layer which is circled in RED, this layer does not really have that much effect.

But i'll explain what textures are assigned here.

Marked A is a translucence map click here to see it in more detail. This layer it just to trying to achieve some sub surface scattering effect underneath the main skin layer.

Marked B is a Diffuse map, I find the maya default renderer tends to fade the textures no matter how deep you make them this map is just trying to keep all the areas like the spots and marks as deep and possible trying to keep as much variation in the skin contrasting light areas with nice dark spots.

Right Marked C is a ramp colour node based on the ideas of Dr Steven Stahlberg's skin shader Link, this is plugged in the the ambient map trying to give a reddish glow coming thought the skin, but you'll hardly notice it.

Marked D take no real notice of this one it's just a few different skin tones taken originally from a good shader by Dr Matt Wood link.

The layer that goes above the bottom layer is circled in YELLOW sorry the hyper shade map is laid out a bit awkward i should of arranged them in the right order but did not really have enough time.

Marked A This is the maya skin shader which you can get of the maya web site Link its very good for bringing out the rice skin tones, but does take some tweaking to get the right look.
Marked B is the colour map of course.
Marked C it's the bump map.
Marked D this is a reflectivity map this brings out some of the nine shiny tones you might want here and there.

Now it may be a bit hard to find but circled in PINK is a transparency map this is used to blend with the bottom layer some areas i want to keep dark as possible other areas i'm happy for the reddish underneath to blend though.

This map just controls the shininess of a shader, I used part if my GI light baked texture Map to help darken a few areas.