I'll show you - gonna take me a little while to prepare screen shots for the tutorial. 

It amuses me that everyone is suggesting some form of blending/partial transparency of the tattoo image with the skin image, and that is precisely what I'm doing. Perhaps you want a greater fraction of skin in the blend. No matter - I leave the artistic choices to you. But straight blending alone with a low fraction on the tattoo simply makes a faded stained look. You lose a lot of the tattoo color and darkness that way. I'm using a couple extra nodes to keep almost all the variation in skin color overlayed witht the tattoo color. But the skin I'm using doesn't have much variation to begin with, so there isn't a lot to preserve. Maybe you want me to actually increase the skin color variations somewhat. I'll show you how. It's really easy.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)