The Abney effect or the purity-on-hue effect is the perceived hue shift that occurs when white light is added to a monochromatic light source.
The addition of white light will cause a desaturation of the monochromatic source, as perceived by the human observer. However, a less intuitive effect of the perceived white light addition is the change in the apparent hue. This hue shift is physiological rather than physical in nature.
In color theory, a tint is a mixture of a color with white, which increases lightness, while a shade is a mixture with black, which increases darkness. A tone is produced either by mixing a color with gray, or by both tinting and shading. Mixing a color with any neutral color (black, gray, and white) reduces the chroma, or colorfulness, while the perceived hue can be affected slightly (see Abney effect and Bezold-Brücke shift).
In the graphic arts, especially printmaking and drawing, "tone" has a different meaning, referring to areas of continuous color, produced by various means, as opposed to the linear marks made by an engraved or drawn line.
View the full Wikipedia page for Tints and shades