While I think you may be on historically rather shaky ground there, I do see what you mean. I'm not sure that there's much pictorial information to be had on the British/Cymric side, but I think you may find some examination of Pictish designs useful; there are a good few sites of interest out there, including:
Pictish Symbol Stones Database
Pictish Arts Society
F. Lennox Campello's Pictish Drawings
Pictish Heritage Links
The Woad Page will tell you all you ever wanted to know about...well, woad, and there is some interesting discussion of the historical record where tattoos and so on are concerned, at:
Period tattoos and body and face decoration.