The mixture is cooked by stirring over heat in a pot or pan. The end result is a thickening and flavoring agent. The final results can range from the nearly white to the nearly black, depending on the length of time it is over the heat, and its intended use.
Light roux lead little flavor other than a characteristic richness to a dish, and are used in French cooking and some gravies or pastries throughout the world. Darker roux, sometimes referred to as "blond", "peanut-butter", or "chocolate" roux depending on the color achieved, add a distinct nutty flavor to a dish and are used in Cajun and Creole cuisine for gumbos and stews.
Preparation of a light roux is rather simple; there is a danger of burning a dark roux, especially if it is attempted over high heat. For the novice cook, pre-made dark roux is available by mail-order and at supermarkets and specialty food stores in some areas.
As an alternative to making a roux, which is high in fat and very energy-dense, to flavor gumbo, some Creole chefs have been experimenting with toasting flour without oil in a hot pan. The results are comparable, but this is a rather difficult technique.