Color is the characteristic of human visual perception, which derives from the stimulation of cone cells in the human eye by electromagnetic radiation in the visible spectrum.
Science of color - chromatics or colorimetry - studies the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of light.
The Red-Green-Blue (RGB) color space corresponds to the three cone cell types that respond to three bands of light:
- Red - long wavelengths, peaking near 570 nm;
- Green - medium-wavelength, peaking near 540 nm;
- Blue - and short-wavelength light, near 430 nm.
The photo-receptivity of other species varies considerably from that of humans. For example, bees are sensitive to ultraviolet but not to red. Some butterflies may have pentachromatic vision. Some shrimps have up to twelve dichromatic units.
Colors visible to humans (with approximate wavelengths and frequencies):
- Red (700–635 nm, 430–480 THz)
- Orange (635–590 nm, 480–510 THz)
- Yellow (590–560 nm, 510–540 THz)
- Green (560–520 nm, 540–580 THz)
- Cyan (520–490 nm, 580–610 THz)
- Blue (490–450 nm, 610–670 THz)
- Violet (450–400 nm, 670–750 THz)
Electromagnetic radiation is characterized by its wavelength (or frequency) and its intensity.
Visible light is with the wavelength within ~ 390 - 700 nm.
Most light sources emit light at many different wavelengths.
Colors of the rainbow - spectral or monochromatic - include all colors that can be produced by visible light of a single wavelength only.
The intensity of a spectral color relative to the context can considerably change its perception.
Color information is transmitted out of the eye by three opponent channels, each constructed from the raw output of the cones:
- Black–White (luminance).
This is why humans cannot perceive a reddish-green or yellowish-blue, although in watercolor, I often divide the pigments of these colors in mixes by particles, to achieve such interesting feel of color extremes.
Value in art is about relative lightness or darkness of colors that is used to create spatial illusions.