Funny enough one of my projects I am busy with is called vascularity. Basically you will be able to add veins to any displacement map, as well as an underlying vein colour for the skin texture on any V4/M4 set. It will come with Psd files so you can create your own. It will be for V4 and M4 UV's.  Most of these displacement maps with veins are not 100% accurate. They are just there to add detail. I have mapped the entire human vein system on a model in zbrush and will translate that into seperate transparent layers for colour and displacement, which you overlay on your favourite texture sets. You can just load the displacement or the colour overlay or both. You will get results like the attached pic above (just an example), where you see a little displacement and the vein colour. But more about that later when it is near completion.

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