Personally I like all black in the engine bay and a body color on the smooth firewall.
I think the Mule has the perfect look with the all black engine area and firewall. I think it all depends what kind of engine you are putting in. If it is a more plain style engine I suggest black. (I am not saying the mule's engine is plain guys). If you are using a lot of chrome and smoothing the inner fenders and firewall it really does look sharp using the body color.
