Very killer idea. I would suggest filling in the white with a color. It would look way better on flesh since you have the really smooth gradual grey shading in my opinion. Unless, of course, you were planning on getting the really killer light grey as well, makign it look exactly like you drew it. That would be effin awesome.
actually the cool part is that the dude thats teaching me how to do tattoos told me that with b/w tattoos you can make the dude bleed a lil more so you can mix the blood with the ink... give it that awsome grummy effect