Within the four color categories, you are likely to find common roasts as listed below. But it is a good idea to ask before you buy. There can be a world of difference between roasts!
Light brown in color. This roast is generally preferred for milder coffee varieties. There will be no oil on the surface of these beans, because they are not roasted long enough for the oils to break through to the surface
Medium brown in color with a stronger flavor, and a non-oily surface. This roast is often referred to as the American roast because it is generally preferred in the United States.
Rich, dark color with some oil on the surface and with a slight bittersweet aftertaste
Shiny black beans with a oily surface and a pronounced bitterness. The darker the roast, the less acidity will be found in the coffee beverage. Dark roast coffees run from slightly dark to charred and the names are often used interchangeably which can be very confusing. Be sure to check your beans before you buy them!
I have tried many different types and liked them all. Some are better at different times of the day. What kind do you like?