Editing Color gel (section)

== Colors ==
Similar colors may vary between different companies' formulations. For example, many have a color named "[[bastard (color)|bastard]] [[amber (color)|amber]]", but the transmitted color spectrum may be different. For this reason it is often misleading to refer to gel colors by name. Even a familiar color name, like Steel Blue, transmits widely differing colored light in each manufacturer's line.  

By necessity, color gels are selected by specifying the manufacturer, line, color number, and name: Rosco Cinegel #3202 Full Blue CTB. 

Apollo Design Technology uses a four digit number based on the [[visible spectrum]] to designate and locate specific color transmissions. 

The GAMColor line from Rosco employs a three digit numbering system, organized by the wavelength of the principle color in the family, i.e.: Blues in the 800's with primary blue at 850 (though the manufacturer's numbers do not relate directly to any wavelength, transmission, or frequency). The same applies to Greens in the 600's, Reds in the 200's, etc.  

Rosco's Roscolux line is currently the oldest major line of color media,   . They started using only a two-digit numbering system, listing colors in no particular order. As the range demanded by designers increased and many more colors were offered in the 1970's and 1980's, two digits quickly proved inadequate. As a result the original scheme was overlayed by three-digit and eventually four-digit numbers in between the original two-digit colors in the line.  

Manufacturers produce swatch books, which contain a small sample of each color, along with the color name and manufacturer's catalogue number. Many manufacturers also provide spectral analysis for each color and transmission values, expressed as a percentage of light allowed to pass through the filter from the light source. Swatch books enable [[designer]]s and [[technician]]s to have a true representation of the manufacturers' range of colors.

Many{{citation needed|date=January 2015}} designers choose a limited color palette for generic applications because it is financially and logistically difficult to have access to all colors for a single show.

[[File:Complex reflectance.svg|thumb|Color correction gels absorb light of some wavelengths more than others. This Rosco gel has a low transmittance at long wavelengths.]]

There are also gels for [[color correction]], such as CTB (color temperature blue) and CTO (color temperature orange). Color correction gels alter or correct the [[color temperature]] of a light to more closely match the color temperature of a [[film negative]] or the [[white balance]] of a [[digital imaging|digital imager]]. Specifically CTB, which is [[blue]] in appearance, will correct tungsten lights that typically have a color temperature in the range of 3,200 to 5,700&nbsp;[[kelvin]]s to more closely match the color temperature of "daylight" negative, which is usually around 5,400&nbsp;K (nominal daylight). CTO, which is [[orange (color)|orange]] in appearance, will correct a "daylight"-balanced light source (such as many common [[Hydrargyrum medium-arc iodide|HMI]] bulbs) to match the color temperature of tungsten negative, which is typically 3,200&nbsp;K. There are "half" and "quarter" variations of the common color correction gels. It is common to use color correction gels for artistic purposes and not just for negative-to-lightsource correction.

Most ranges of gels also include non-colored media, such as a variety of [[diffusion]] and directional "silk" materials to produce special lighting effects. "Opal" for example is an [[opalescence|opalescent]] or [[translucent]] [[diffusion filter]].

It is common for a gel manufacturer to publish the [[transmission coefficient]] or even the spectral [[transmittance]] curve in the swatch book and catalogs. A low transmittance gel will produce relatively little light on stage, but will cast a much more vivid color than a high transmission gel, because the [[colorfulness]] of a light source is directly related to narrowness of its [[spectral linewidth]]. Conversely, the flatter its curve becomes, the closer the gel is to a [[neutral density filter]].