Helmholtz–Kohlrausch effect

The Helmholtz-Kohlrausch effect is an entopic pheonmenon wherein the intense saturation of spectral hues is perceived as part of the color's luminance. This brightness increase by saturation, which grows stronger as saturation increases, might better be called chromatic luminance, since "white" or achromatic luminance is the standard of comparison. It appears in both self-luminous and surface colors, although it is most pronounced in spectral lights.

References

The geometry of color perception] Quantification of the Helmholtz-Kohlrausch effect for CRT color monitors LED Projection Enters the Mainstream