Most of us think to dress up for grand occasions that specify black tie on the invitation, but those are not the only evenings when we should take some care. The well-dressed man ideally changes his clothes any time he goes out at night, even when going out is nothing more than going down for dinner in his hotel. And to me, that means he should be wearing something that will complement a woman's black cocktail dress (this will be particularly useful when he's with someone who's wearing one). Not black tie, but not a typical business suit either.
The late Hardy Amies called this intermediate formality "late day dress," and it's accomplished with either a blazer or a peak lapelled suit in a luxurious material. For either choice, the ideal color is not dark navy but something closer to a French blue, with a green cast to it instead of a red. It's a nice look for the late afternoon sun, it turns appropriately black under artificial light, and it combines well with black shoes and a white shirt under either condition.
Dress up the blazer with a bow tie, or the suit with a satin four in hand. And that's late day blue.