There aren't many hard-and-fast rules when it comes to menswear, but matching your belt to your shoes seems to have been one of them for as long as dudes have been suiting up.
But here's the thing: it's not that simple anymore. And that's a good thing.
The Old Rule
"Thou shalt match the leather color of your shoes to the leather color of your belt."
Dark brown shoes? Dark brown belt. Black shoes? Black belt. Keep the shades identical and never, ever, ever, ever pair across color lines.
The New Rule
Mix it up — but with caution.
That combo above of a light brown belt with dark brown wingtips is just fine. Playing with different shades of your leather color — a dark chestnut watch strap, a sandy brown belt, and rich amber lace-ups — is a good way to add a slight amount of visual contrast to your outfit, so long as the shades aren't jarringly different.
There is a caveat, though, and it's a big one: mixing brown and black is still (mostly) off-limits. If it's incredibly subtle — like if you're wearing black leather shoes and your belt is so dark a shade of brown that, at first glance, it seems to match — then you get a pass, but it's not something you should aim for.