Chrominance key Chrominance key is sometimes known as C80 (Colour Separation Overlay). This technique relies on colour to create the hole. Typically blue or green is used in television. As with luminance keys, two source video streams are needed: one the background, the second the chroma key foreground. A common instance where chroma key is used is with a television presenter Here the presenter is shot against a chroma key blue background and keyed over either computer-generated graphics or a video image of a different location. The two, when keyed together, give a composite where the presenter appears to be in front of a background image.