As the last pilot to get into the RN with glasses (DCI changed the loophole the second week I was at Dartmouth !!!), I've lived with the problem for a while
Currently I have graduated bifocals, both clear and RayBans, plus a "straight" non bi focal set of prescription RayBans. The latter are most important, it took me years to realise that my inaccuracies in sling loads/fire bombing was resolved when I stopped trying to see the ground through the reading segment of the glasses
Similar problem as Nigel for night ops, or when the instrument panel is in deep shadow.
Colours for sunnies? Personal preferences will always take over, but brown works best for me.