Wearing black suits before 6pm has traditionally been appropriate only at funerals. For some reason though, more and more people seem to be wearing black as their main business suits. I can't fully explain its popularity, but I think it may partly be the increasing association of black suits with attractive celebrity men.
The trouble is that it's easier to look good in a black suit when you're trim and tanned and wearing a white shirt open at the neck, and also when you're mostly photographed in the evening clutching a cocktail. For those of us who have a healthy English pallor and mostly wear suits in a city boardroom, black is less of a good choice. It flatters few men's skin tones and, while you may think it is a 'safe' colour, it actually doesn't serve as a particularly good background for coloured shirts, ties, or pocket squares.
Dark grey or dark blue is a far more stylish choice for daytime, especially if you only own a couple of suits. There may well be a time to add a black suit to your wardrobe but it's only going to come when you've got the basics covered and, when it does, you still probably want to keep black mainly for evening events.