HSL and HSV are both cylindrical, with hue, their angular dimension, starting at the red primary color at 0°, passing through the green primary at 120° and the blue primary at 240°, and then going back to red at 360°. In each, the central vertical axis comprises the "neutral", "achromatic", or "gray" colors, ranging from black at lightness 0 or value 0, the bottom, to white at lightness 1 or value 1, the top.