Color Temperature Reference Chart
Digital cameras and film are sensitive to the temperature of light and are measured in Kelvin (K). Daylight temperatures are about 5,000 to 5,500 degrees K and at this temperature, the light appears 'white.' Warmer light sources, such as incandescent filament-light, is colored at a longer wavelength, usually about 3,000K.
Warmer Colors (Red)
3000K Incandescent and Warm-white Fluorescent
3700K White fluorescent
5000K Day-white fluorescent
5200K Direct Sunlight (white)
5400K Electronic Flash
6000K Cloudy/overcast (trending Blue)
7200K Mercury Vapor, high-temp)
8000K Deep Shade (under a bright blue sky)
Cooler Colors (Blue)
In photography, color temperatures can be seen in the final prints. For example, photographing under deep shade can give the photographs a distinct blue tint. This can be corrected by using the digital camera's built-in white-balance (with film, use a warming filter). Photographs can also be corrected in post-processing, using a photo-editor.
Note: Color temperature is not the wavelength of a specific color (measured in nanometers 600nm, etc.).
See this imageLiner.blogspot.com article on DSLR White Balancing / Color Correction
In practice, older fluorescent lighting displays an unpredictable color spectrum that is hard to color-correct; often with simultaneous greens, yellows and blues. Newer fluorescent lighting has a more predictable color spectrum and are often advertised with their color temperature. However, some brands mistakenly show the color temperature as "Lumens" (e.g. GE branded lamps report 2700 Lumens; should be 2700K).
Setting Exposure with an 18% Grey Card