1. Method for mixing two colour television signals comprising a foreground signal sensed by a foreground camera and a background signal, comprising deriving a switching signal (WS) as a function of the colour of the foreground signal by providing a first switching signal when the colour of the foreground sensed by the foreground camera differs from a selected background colour and a second signal when the colour sensed by the foreground camera is effectively only that of said selected background colour; desaturating selected portions of the foreground signal while maintaining the luminance component thereof substantially unaltered during occurrence of said second switching signal; at least partially suppressing portions of the background signal during occurrence of the first switching signal; and adding the selectively desaturated foreground signal and the partially suppressed background signal.