The colors of the visible spectrum are violet, blue, green, yellow, orange, and red. Because light travels in waves, it has both frequency (the number of waves that pass a given point in space during a specific time interval) and wavelength (the distance between any two corresponding points on successive waves). It's not crucial for you, as a designer, to know the frequency and wavelength of each color, but we're going to tell you anyway:

Color Frequency Wavelength Violet 668–789 THz 380–450 nm Blue 606–668 THz 450–495 nm Green 526–606 THz 495–570 nm Yellow 508–526 THz 570–590 nm Orange 484–508 THz 590–620 nm Red 400–484 THz 620–750 nm Image courtesy of Wikipedia Commons

Note that frequency and wavelength are inversely proportional. The higher a color's frequency, the shorter will be its wavelength.

• Additive mixing happens when two or more differently-colored lights are aimed at the same surface.
  
• Subtractive mixing happens when a single light source shines through differently-colored filters. Each filter allows certain colors to pass while blocking or absorbing other colors.
  

In additive mixing, primary colors are those three colors which, when aimed at the same place at the same intensity, theoretically form white light ("theoretically", because in practice, this is limited by the imperfections of color filters and light sources). These colors are red, green, and blue.

The secondary colors in additive mixing are those colors which can be created by evenly mixing two primaries. These colors are:

• Cyan (blue and green)
• Magenta (blue and red)
• Amber (red and green. Really.)

This sentence is 100% red.

This sentence is 100% green.

This sentence is 50% red and 50% green (See? I told you).

Additive Mixing	Subtractive Mixing

In subtractive mixing, the primary colors are those which can be created by evenly mixing two secondaries, as shown in the drawing above. In the example on the right, a white light is altered by inserting a cyan filter, which absorbs the red part of the spectrum and passes (or "transmits") blue and green light. The resulting cyan light is then passed through a yellow filter. This filter absorbs blue light, but transmits any red or green that may be present. Since there is no red (because we've already blocked it with the cyan filter) all that is transmitted is green.

Subtractive mixing is often found in automated fixtures. The act of inserting a color filter in front of a light is a very simple form of subtractive mixing.

Complementary colors are those colors directly across from each other on the color wheel:

For example: yellow and blue are complementary to each other, as are green and magenta. As you can see, the complementary of any primary color is the secondary color formed by mixing the two remaining primaries.

Complementary colors, when combined additively on a neutral surface, form (in theory) white light.

Complementary colors, when used adjacently, reinforce each other; each makes the other appear to be more vibrant.

Jeff reminds you that the color wheel shown in the above link is subtractive, for mixing paint, not additive, for mixing light.

For this photograph, the white balance was set to "daylight" (or "outdoor").	For this photograph, the white balance was set to "tungsten" (or "indoor").

Color temperature is measured in "degrees Kelvin," abbreviated as "K." As mentioned above, the bluer a light is, the higher its color temperature will be. Below is a table of approximate color temperatures for common light sources:

So what does this mean? From what are these numbers derived? The temperature is referenced to that of a standard "black body" – a block of carbon which, when heated to specific temperatures, emits light of specific colors.

The Kelvin scale (named after British physicist William Kelvin) is a variation of the Centigrade/Celsius scale, except that rather than its being keyed to the freezing point of water, it is based on "absolute zero". If you subtract 273 from a Kelvin temperature, you will have its Celsius equivalent.

You may be thinking that none of the colors above looks like "white".... and you're right. First of all, they are merely approximations and not, as such, accurate. Secondly – and more important – the eye (or, more accurately, the brain) adapts. We tend to automatically "white balance" ourselves to the dominant light source in our environment at any given time. If, for example, you spend a significant amount of time outdoors during the daylight hours and then go into your house or apartment, the interior lighting may look yellowish for several hours, until your brain "white balances" to its new environment. This is something you should remember, by the way, when you're writing the first few cues of your show.