A plurality of electronic gaming machines are interconnected over a network to a central computer. Each gaming machine generates a composite video signal formed from at least two video signals. A first video signal carries game graphics information for generating at least a still graphics display which moves at selected times during play of the game. A second video signal carries video information for generating a moving video display. The two video signals are combined in accordance with key color information, which is carried by the first video signal. The combining is selectively controlled by the central computer. The central computer may also select which one of a number of second video signals may be combined with the first video signal. The central computer may also select a particular key color from a plurality of key colors defined in said key color information so as to control where on the display unit that the combining takes effect.