well, warhammer vermintide is an FPS
http://media2.giga.de/2015/10/warhammer-end-times-vermintide-titelbild-rcm480x0.jpg
Maybe if it would be possible to have like, the awsd keys in red, and the rest in green with the top row in the gold-ish color of the warhammer logo?
And also the Q in a gold or teal color as this is a key to fast switch between weapons. And E is the use button.
With sometimes a few streaks of brown (that would signify rats) that would scurry around the green parts?
Need some more info?