The shade of wood grain bookcase that is darker is typically oak. Oak wood, known for its rich and robust grain pattern, tends to have a darker appearance compared to other types of wood. This is due to the natural coloration and density of oak, which contributes to its darker hue. Oak wood contains more tannins, which give it a darker color and a more durable finish. Additionally, oak wood is often stained or finished with darker stains to enhance its natural beauty and depth. According to the American Hardwood Export Council, oak is one of the most popular woods for furniture due to its dark, rich grain and durability.