Which of the following is classified as a dark sauce?

Bordelaise is classified as a dark sauce due to its rich flavor and deep color, which typically comes from the use of red wine and stock, often made from beef or veal bones. The sauce is named after Bordeaux, a region in France known for its red wines. The method of creating Bordelaise involves reducing red wine and combining it with a velvety demi-glace, which is a dark sauce made from reduced brown stock. This technique intensifies the flavor and gives it a dark appearance, characteristic of dark sauces.

In contrast, other sauces listed do not fit the classification of a dark sauce. Beurre Blanc is a creamy, emulsified sauce made from butter, wine, and vinegar, resulting in a pale color. Roux, which is a mixture of equal parts of fat and flour, serves as a thickening agent and is typically light in color. Tomato sauce, while it can have a robust flavor, is generally lighter compared to traditional dark sauces and is often regarded as a red sauce due to its tomato base.