A roux is a mixture of flour and butter or oil. You stir the mixture until it reaches the desired color. I make a blond roux for my crawfish etouffe, but this is the roux I use for gumbo. It has a smoky, nutty flavor. I used to stir the roux for my mom when I was growing up. You stir for a very long time, because it burns easily. I would always ask if it was the right color yet. She would tell me it needed to be the color of her coffee with just a little milk or she would find a penny and set it on the counter next to the stove so that I could see when it was the “right” color.