None of the five million black-and-white sets already in American homes could receive a color signal, so RCA hid it inside the one they already understood: three electron guns, one per color, each encoding its picture to nest invisibly within the existing black-and-white broadcast, decoded only by sets built to look for it. The color camera behind it split incoming light through prisms into red, green and blue signals, and the compatible trick reached households in time for The Wizard of Oz’s first color broadcast in 1956.