Personally, I don't like belted trousers. They ride too low under a jacket for my taste and the buckle is distracting to the eye. But I did wear them as a young man, most men wear them today and some of those men have asked about them. So I have a few thoughts to share.
First, belts should complement your shoes. That means black calf shoes should be accompanied by a black calf belt. A man doesn't have to match his browns precisely, but when he wears brown shoes his belt should be brown. And I believe that if one is going to the trouble to wear burgundy or suede shoes, one should go to the trouble to wear a burgundy or suede belt.
That said, the most important thing I ever learned about belts was that the same people that make shoes offer them, in the same shades of leather as their shoes. You have to look - makers from Alden to Edward Green don't make much of their belt making. But the expedient way to have belts that complement your shoes is to buy them where you buy those shoes. Provided, that is, that you shop at factory stores. For some reason, many department stores don't seem to buy belts from the same places they get their shoes. But then, who would want pink alligator belts anyway?
Belts from their shoemakers will be all most men require in their lifetimes, but some always want more. And, in the case of belts, that leads inexorably to the skins of various reptiles, flightless birds, and certain denizens of the sea. Leathers from these creatures is turned into lovely straps in a plethora of colors by skilled artisans such as Hermes or San Francisco's April in Paris (source of the belt in the photo), and the straps themselves may be combined with buckles that cost as as if they were made from solid gold. Probably because some of them are.
I've never understood the fascination with alligator or crocodile belts, particularly since many of the men that wear them think shoes from the same material too flashy. Which of course, makes it more difficult to find shoes that complement that stingray creation around your waist. But, in a world where logos are the easy substitute for good taste, I don't call that a sin.