We saw no tails running about the ship on formal night. Men wore black tuxedos and the you saw the occasional white dinner jacket as well. There were at least dozen men running around in Kilts (which looked pretty cool). There wer some men who wore black suits but no one in light colored suits. Anyone connected with the military, wore their dress uniforms.
As above but It does depend on type of trip slightly:
Round trip Cruises out of Southampton tend to have more English people on board so you will see quite a few white jackets on these, especialy amongst the older passengers.
Transats, where most passengers are American, mostly black Tux.