be careful how much brown OR orange you use. I know the following may be a littl eodd but... before deciding how to do the yellow I think you have to decide whatthe accent color will be.... My imp fists are 5th company and have black as their company color. I highlight the black with dark blues as opposed to greys.
If I were to highlight or use orange or brown with that kind of black I would get a real mess. The black would seem way out of place.
If you are planning to use red as the accent color (I think that is 3rd company) then you are okay.
I have been base coating white, layer of golden yellow, a black wonder wash to add depth, then a heavy drybrush of golden yellow, then a highlight of mixed golden yellow and skull white.. then if it needs it a further highlight of skull white on the extreme edges.
No brown OR orange because of the black.
ender502