The color detector circuit can be adjusted with essentially infinite variability to cause it to detect virtually any color in the visible spectrum, and to define a narrow passband or range of colors which the device will transmit. The device can be used to provide accurate color key signals with a variable...http://www.google.co.uk/patents/US4811084?utm_source=gb-gplus-sharePatent US4811084 - Video color detector and chroma key device and method
