Coffee beans are coffee beans. There is not something called a light
coffee bean and dark coffee bean when they are harvested. What makes
the beans light, medium, or dark is the roasting process.
The degree of roast affects coffee flavor and body. The color of coffee
after brewing is also affected by the degree of roasting. Darker roasts
are generally bolder because they have less fiber content and a more
sugary flavor.
Roasting does not alter the amount of caffeine in the bean, but
does give less caffeine when the beans are measured by volume because
the beans expand during roasting.