I tall depends on the septs, etc.. Actually, a good place to look for idea off the top of my head is the Dawn of War army painter, Peruse the skisn there to get an idea of how the different colors are painted on. If the septs there don't match the color he wants, he can even swap the (for example) blue/white on a sept for... red/gold or something. Though Tau are usually in my experience in primary colors, no metallics.
__________________  "Truth is infinite. It is defined by our perception of the facts; therefore we can never know absolute truth, we can only guess at it. A man who knows he has done no wrong needs no redemption, regardless of the views of others. The truth is what he believes it to be. A man who knows he has done wrong can only be redeemed when he chooses to forgive himself."
-Lord Inquisitor Balkoth
Black Saints Adeptus Astartes Chapter |