LOR QUALITIES.

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

+HUE is the name of a color.+

(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 LENGTH 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.[6]

[Footnote 6: See Glossary for definitions of Micron, Photometer,
Retina, and Red, also for Hue, Tint, Shade, Value, Color
Variables, Luminosity, and Chroma.]

+VALUE is the light of a color.+

(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[7] scale of value places all colors
in relation to the extremes of white and black, but cannot describe
their hue or their chroma.

Science describes this quality as due to difference in the HEIGHT or
amplitude of ether waves impinging on the retina. Small amplitudes of
the wave lengths given in paragraph 21 produce the sensation of dark
green and dark red: larger amplitudes give the sensation of lighter
green and lighter red.

[Footnote 7: See Photometer in paragraph 65.]

+CHROMA is the strength of a color.+

(23) Chroma is the quality by which we distinguish a strong color from a
weak one. To say that a rug is strong in color gives no hint of its hues
or values, only its chromas. Loss of chroma is loosely called fading,
but this word is frequently used to include changes of value and hue.
Take two autumn leaves, identical in color, and expose one to the
weather, while the other is waxed and pressed in a book. Soon the
exposed leaf fades into a neutral gray, while the protected one
preserves its strong chroma almost intact. If, in fading, the leaf does
not change its hue or its value, there is only a loss of chroma, but the
fading process is more likely to induce some change of the other two
qualities. Fading, however,