In a large skillet, melt the butter or other fat over medium-high heat.
Slowly but gradually stir in the flour and cook to the desired color and flavor. For a white roux, cook no more than five minutesFor a blonde roux, cook no more than 5 to 10 minutes.For a dark roux, cook 10 to 30 minutes.
A white roux is cooked the least, no more than 5 minutes, so it remains light and is mostly used with a milk base (think Béchamel, one of the five mother sauces).
When making a blonde roux, the fat & butter is cooked out to a golden color, 5 to 10 minutes, taking a little more time to make than a white roux. Because of this, it will have more flavor than a white roux.
A brown roux is cooked between 10 and up to 30 minutes. Brown roux are great bases for meat gravies and are used as an ingredient in another mother sauce, Espagnole.
Dark brown roux is used in traditional gumbo. Another 10 minutes can be added to the cooking time for this.