The correct answer is value.
Hue is the color’s name, such as red, green, or blue. Saturation is the intensity of the color, or how much white is mixed in. Value is the lightness or darkness of the color, or how much black is mixed in.
Metamerism is the phenomenon of two objects having the same color appearance under one illuminant but different color appearances under another illuminant.
Gray scale is a series of shades of gray, ranging from black to white.
Shading is the application of light and dark to an image to create a sense of three-dimensionality.
I hope this helps!