The umbrella term "illustrative" is as broad as can be. Traditional has its specific guides, watercolor may have a looser connotation but still has a set of rules to be followed. Illustrative has become the term used for tattoos that seem to defy a lot of the categories available; the work has roots that spans the tattoo world and the art world in different ways than its forbearers. Robson Carvalho's illustrative style comes with a ton of adjectives: sketchy, loose, watercolor-inspired, pastel-like. His tattoos look like a page lifted directly from his sketchbook, and often times, they are.
Translation from paper to skin is what a tattooer does best, but being able to make a tattoo's shading and line work reminiscent of what occurs on paper is quite a feat. Skin, put simply, just isn't like a thick piece of cold-press watercolor paper or trace vellum. When you lay your pen down on the grain of paper, ink spreads, bleeds, flows. Whereas with a tattoo needle, there's precision — to create what looks like an ink blot, you have to physically recreate the ink blot from your drawing/stencil.
Carvalho's tattoos capture that loose pen work. His art looks like he took a sharpie and brush out, rather than a tattoo machine, and sketched up a doodle. The perfection comes from the imperfection; some lines fade out, some colors wash away, some ink sprays as if the pen nib tripped itself up.
Carvalho's use of color lands in the watercolor style, but really looks like he snagged himself a huge box of Prismacolor pencils and carefully faded each color into the next. His limited palette coupled with his loose line work makes for some really dreamy, ephemeral imagery, leaving much to the viewer's imagination.