Tattoos

http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3093841

Decals

http://www.runtimedna.com/forum/showthread.php?31709-Dual-Materials-with-Stencils

And a little more explanation of how the Blender node works:

http://www.runtimedna.com/forum/showthread.php?39937-Blender-Node-Question

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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)