This trick allowed the Apple II to display up to 16 colors. Compatibility was achieved by encoding colour info in the type of a high-frequency sinusoidal signal. The phase of this signal at a given level, relative to a reference signal (the “colorburst”) transmitted earlier than each row started, decided the colour’s underlying hue. The amplitude of the signal decided how saturated the colour was. Originally, U.S. broadcast television was black and white only, using a fairly easy standard known as NTSC .