while most guys do seem to like the double blue/blue/greene family of rubber these days, I've still be getting good results running black fronts with grey rears. It's a pretty fine line though, because my car always seems to push too much if I use greylo rears instead of greys. So, for me, black fronts in combination with grey rears feels nicely balanced, grippy enough to be comfortable, and yet and free enough to be competitively fast. And it sure doesn't hurt that the black/grey family of rubber seems much less prone to picking up carpet fuzz off the track, so the balance stays pretty much the same from the beginning to the end of each run.