Always remember that formality of dress shoes begins from the darkness of its color. For example, black is always the most formal color while light brown is the least formal. So you should match your shoes against your suits or pants based on the occasion. If you are attending a formal business dinner, then naturally black shoes are your ultimate choice rather than brown shoes.
Of late, there are more men wearing light brown or camel colored dress shoes against their dark colored suits or pants. These high contrast creates a very trendy style which I personally like. However, we should also note that this combination gives a more casual feel toward it.
What if the suit or pants are brown-based colors like olive or chocolate colors? Must we definitely wear it against brown shoes? Not necessarily, black shoes are just as fine. Of course, brown shoes would let the color flow very smoothly but black is still a color that can fit nicely. Remember that black is the color for formal.
Lace-up shoes are one step better than slip-ons for their formality. At the same time, lace-ups are split into Balmoral and Blucher types. Refer to Mens Dress Shoes Styles for their differences. The latter is always considered less formal because of its open throat design.
So remember that whether you want a formal or casual look would depend on your choice of two criteria: the dress shoe style and its color.