A color's 'quality' is its hue position in the color circle; its 'quantity' (brilliance) is its lightness or darkness

Itten uses precise terminology: ‘quality’ of a color = its chromaticity — its position on the color circle, its family identity as green, red-violet, etc., regardless of how it is tinted or shaded. ‘Quantity’ or ‘brilliance’ = its luminosity level, from white to black. These are independent dimensions. Two colors can share the same quality (hue) but differ in quantity (one tint, one shade); or share the same quantity (equal brilliance) but differ in quality. Distinguishing these prevents confusion: simultaneous contrast and cold-warm contrast are best studied with colors of equal brilliance (eliminating light-dark as a variable). The natural brilliance of saturated hues differs: pure yellow naturally sits near the white end; pure violet near the black end. When a saturated color is lightened or darkened to match another, it loses its identity as a ‘pure’ hue.

Examples

In code: HSL separates these — H = quality (hue angle), L = quantity (lightness). Setting all colors to L=0.5 equates their brilliance for pure quality comparison. Saturation S is a third dimension separate from both.

Assessment

Given ‘dark red’ and ‘light red’ — do they share the same quality? Same quantity? Explain the difference between brilliance and saturation; state why equal-brilliance exercises isolate the quality dimension.