I don't have a favorite combination because no matter what colors you choose, it doesn't change the colors at all.
And on a related note, they did remove the dials from the standard cars' cockpit views. They now use the same HUD gagues as the premium cars do which are not the same type of display(not dials) and cannot change color... hence my lack of a favorite. I'm not sure why you can change the color scheme on one and not the other, but I guess it's for the usual reason: because PD. A very minor annoyance at most, I'm not going to lose any sleep over it. I'd much rather we could adjust the opacity of the HUD and move things around and change the gap times to something more useful. A button to toggle all of it on/off on the fly would be nice too.