Color Theory is the combination of multiple colors, RGB, to create a color pallet of multiple shades, hues, etc of different colors. This pallet is used for programs such as final cut, adobe products, etc and is the basis for compositors in movies and CC (Color Correctors). A whole career can be made off of color correction which is how the movies/ cinema create that HollyWood look. (I.E. Cop movies have that blueish tint to them, beach movies have a sun bleached look to them) this is all done by color theory and the use of blending.
Color Theory can be applied to Keying, which is the ability to remove a color and allow it to be transparent using it's alpha channel to see through the layer. The keying plug in or module can allow the user to select any color to key but the most efficient and effective of those would be green or blue. Green stands out and less of a skin tone color so less "spill" onto the foreground surface. These keying techniques can be perfected using simple additional plugins such as Chokers, White and Black Gains, Balance function and edge blur.
-Tim
