So, while painting sometimes things go wrong. I've been painting a mass of Plains Indians for Pony Wars and my daughter asked me if I had meant to put blobs of various colours onto their faces. After a moment of verification I was inspired to say "yes, of course. It's warpaint!" 

While my daughter wasn't really fooled, and it might save me a touch-up job in some cases, it started me thinking. I wondered if there are any other armies where "warpaint" or similar might be a good excuse for accidental slips of the brush. 

Anyone have any ideas?

Britons and Picts immediately come to mind

If not, war paint I’d use “they are tattoos” or there is always that great historical documentary film Braveheart to show woad :-) .   Blackened faces/bodies has been used for centuries the Germanic tribe Harii come to mind (who liked to do most of their fighting in the dark).

Just out of curiosity I’m about to paint my Plains Indians what option did you go with for skin tone?  I’m looking at going with Vallejo Dark Flesh as a base.

I've got a few Celts with deliberate woad-painted skin, and at second glance one or two of the other Celts also have "tattoos" now that I look at them closely. I really must pay more attention to touching up. :-)

I might have to put together a warband of Harii. That way I can leave most of the black undercoat showing through! 

For the Plains Indians I've used Burnt Sienna, sometimes with a touch of crimson to redden it up a little.  Doesn't need to look that realistic as a skin tone, more like 1950s film make-up - in true Pony Wars style.