No, Giyu Tomioka's sword, known as a Nichirin Blade, is not black. The color of Giyu's Nichirin Blade is a light teal or turquoise, often described as a water-like color. The blade itself is a bright shade of blue-green, while the hilt and guard are silver. The specific color of Giyu's sword is consistent with his water-based Breathing Technique and serves as a visual representation of his abilities.