After reinforcing the lack tattoo patterns I painted in the highlights using Cadmium Red Light & Titanium White and Payne's Grey and Titanium White. While it would seem correct to paint the tattoos on after you've rendered the figure (since tattoos are printed ON the surface of the skin) it actually DOES look "drawn on" if done that way. By painting around the tats it integrates then into the figure giving them a more organic feel. I also like that they kinda look like they were carved into his skin before being filled in.
Your logic actually makes a lot of sense. When a tattoo is applied, a layer of skin will heal over the tattoo-this is why people of darker persuasion have a hard time with colors. Its basically the color of the tattoo ink plus the color of the skin in that particular area, so you would almost certainly have a slight red cast to tattoos applied to a red skin. Thanks again for the highly informative tutorials, and the great Art!