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(20) The three color qualities are hue, value, and chroma.

(21) Hue is the quality by which we distinguish one color from another, as a red from a yellow, a green, a blue, or a purple. This names the hue, but does not tell whether it is light or dark, weak or strong,—leaving us in doubt as to its value and its chroma.

Science attributes this quality to difference in the of ether waves impinging on the retina, which causes the sensation of color. The wave length M. 5269 gives a sensation of green, while M. 6867 gives a sensation of red.

(22) Value is the quality by which we distinguish a light color from a dark one. Color values are loosely called tints and shades, but the terms are frequently misapplied. A tint should be a light value, and a shade should be darker; but the word “shade” has become a general term for any sort of color, so that a shade of yellow may prove to be lighter than a tint of blue. A photometric scale of value places all colors in relation to the extremes of white and black, but cannot describe their hue or their chroma.