A big consideration to make when wearing a casual belt is whether you want it to be an accent piece or a centrepiece. An accent piece is subtle, low-key, and complements the rest of your outfit. It’s usually in coordinating or neutral colours. A centrepiece demands attention and contrasts with the rest of your outfit.
While dress belts are pretty much always accent pieces, casual belts can be accent or centrepiece accessories. There’s nothing wrong with either approach. You just want to dress appropriately for the effect you want.
A good accent belt should share some of the characteristics of the other pieces in your outfit. Similar or matching colours is an obvious choice just as how most people generally select their belts and shoes.
A casual belt should still match your metals, but you’ve got more leeway on the leathers — brown with tan or tan with white is fine. Of course with casual outfits, you’re often not wearing leather at all — either in your shoes or in your belt. You don’t need to match the colour of a casual belt of leather, or any other material, with the colour of canvas/cloth sneakers. Let the colour of the belt work with your overall get-up; when in doubt, go with brown.
Centrepiece belts, on the other hand, are there to provide deliberate contrast and provide a sharp, divergent punch of colour or style compared with the rest of your get-up. They work best when the rest of the outfit isn’t too filled with colours and patterns. One or two bright elements are enough — more just looks too gaudy and busy. Keep in mind that for belts as your outfit centrepieces, you don’t want to wear an eye-catching statement belt if you’re not confident about drawing attention to your waist!