From what I have seen the majority of colours used here are black, red and white, is other acceptable, or maybe more specifically is there a non-navarri colour?
I also wondered about where these paints should be. I noticed the majority being on ones face but is this essential or can I just have it on an arm or around my neck?
everyone has their own style and way they like to do it. Some are epic, some are if people are like me too bloody lazy to use paint brushes so need help from other people to paint me up or I finger paint. colours can be seen in the navarr wiki. Plus I find if someone else does warpaint stuff its like a little bit of a bonding session
My binding of thorns is green vines with red thorns and thats not unusual
I would avoid any “modern” colours, and some could be very hard to obtain IC and there fore people will ask about them. Purple as an example is an expensive pigment historically. I had always been tempted to do the brands as scarification or branding. To show an excessive urgency in the need. IE war party gone horribly wrong and someone stepping up.
I was considering using purple so this is a very good message 
Please don’t misunderstand that by people asking about it is a bad thing. Use purple. Have people ask questions, have reasons for it to be purple. I would avoid the lighter purples and keep to deeper shades and such. I would suggest nothing lighter than the purple used by civil servants.
Purple shouldn’t be too hard to get, nor any other colour.
“The Grendel enjoy bright colours, especially purple. Purple dyes were once rare in the Broken Shore and only the wealthiest Grendel could afford them. In modern times they have become common-place as a result of trade, but they remain prized for their historical association with wealth and power.”
The joys of global trade. We’re the best of the best in the Empire, if we attend Anvil, and trading with, say, the Sarcophan Delves for purple dye isn’t really the hardest thing, and that’s even assuming we don’t have it here in the Empire naturally, given our imperial colour is purple.
So there are some barbarians similar to Navarr who have predominantly green and yellow tatoos but having said that each tatoo is personal. Do what you would like, avoiding big chunks of blue (so you dont look like mel gibson) is a good way to go but natural colours (dont forget there are birght flowers) are all good.