Janka Hardness Rating 1010 - Also known as Black Walnut or American Walnut, this wood species usually has fine, straight graining and coloring is a rich, almost chocolate brown. Homeowners like the natural color of Walnut flooring and the warmth it automatically adds to a room. There is some color variation from board to board, as the sapwood can range from light tan to medium brown Walnut hardwood flooring can be a character grade showing knots and other grain variations.