Value

Value is how light or dark a color appears, regardless of its hue. High-value colors are light*, while a low-value color is dark*.

Flipping a photo of the color into grayscale reveals the value level of the color.

Two different hues can have very similar values even when they look very different in color.

For instance, a yellow with a value of 5 is the same value as a level 5 purple even though we tend to think of purple as a darker color than yellow. In grayscale, same value colors look like the same gray.

For more on value, see contrast.

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*Copic Markers notoriously run opposite. The last number on the marker cap indicates color value. In Copic, high last numbers are dark while low last numbers are light.