For me, any darker shades of blue I find is more for business then anything else. Â Also can act as an afterwork social gathering(ie. drinks after work) but I find daker greys to be much more versitile.
Gray is in one sense more versatile, since it is not a color but is "neutral." Â Many more colors and color combinations can therefore be worn with it. But the original question was about formality. Â I think the most formal non-tux suit a guy can wear is a midnight blue DB. Â For "somber" occasions, very dark gray works better, in my opinion. Â Though no one should feel guilty about wearing a dark blue suit to a funeral. Â But in my opinion, color -- any color -- is always going to be slightly more "festive" than dull old gray.
Lighter shades of blue just doesn't look right for a suit, IMHO.
Cerainly powder or robin's egg blue would look ridiculous for a man's suit, the sole exception being seersucker. Â But slate blue or a medium shade of blue-gray is just fine.
As a rule of thumb, the cleaner the style and the darker the color, the more formal it is.
I remember reading blue pinstripes as the ultimate money suit.
I'm not sure what a "money suit" is, but solid dark blue or grey is more formal than the same shade with stripes. Â I would even say that a medium dark gray solid is more formal than a very dark gray with a stripe. Â I would not, however, say the same thing about cambridge gray or slate blue.
I think black is not appropriate for business and best reserved for occasions such as a party, a wedding(evening, night) and funeral.
I just don't like black for suits, no matter what the occasion. Â I think black should be reserved for formal wear. Â I'm a traditionalist, I guess.