The hue of a color places it on the color wheel where the color spectrum (rainbow) is evenly spaced. Each hue corresponds to a particular wavelength in the portion of the electromagnetic spectrum that is visible to the human eye.

Electromagnetic Wavelength

Here are the approximate range of wavelengths (in angstroms) for each of the usual rainbow hues:

Color Wheel Basics

Here is a common color wheel with 12 hue gradations. There can be more or fewer gradations.
CHART: The common color wheel
Primary hues are red, yellow, and blue. See Systems for a discussion on additive and subtractive primaries.
CHART: rimary hues or colors
Secondary hues are formed from the primary: orange (red+yellow), green (yellow+blue), violet (blue+red).
CHART: The secondary hues or colors
Intermediate hues (tertiary) are formed from adjacent primary and secondary colors, eg yellow-green is formed from yellow (a primary color) and green (a secondary color).
CHART: Intermediate hues or colors
Cool hues range from green to violet.
CHART: Cool hues or colors
Warm hues range from red to yellow.
CHART: Warm hues or colors
Analogous hues lie side by side on the color wheel, eg red, red-orange, and orange.
CHART: Analagous hues
Complementary hues lie directly opposite of each other on the color wheel. EG: Red and green.
CHART: Complementary hues or colors

Hues of Color Systems

In the color wheel, the primary hues are RYB (red, yellow, and blue). These hues are subtractive (removing colors brings it closer to white) in this manner:
CHART: RYB, the primary hues or colors of the color wheel

In most print, the primary hues are CMY (cyan, magenta, and yellow). These hues are subtractive (removing colors brings it closer to white) in this manner:
CHART: CMY, the primary hues or colors in print

In most video, the primary hues are RGB (red, green, and blue). The hues are additive (adding colors brings it closer to white) in this manner:
 CHART: RGB, the primary hues or colors of video

The Munsell color system specifies hues on the color wheel using 3 notations:

The Ostwald color system specifies 24 hues on the color wheel. The 8 groups are yellow (1,2,3), orange, red, purple, blue, turquoise, seagreen and leafgreen.
CHART: The 24 hues or colors of the Ostwald color system

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