The number of colours in a display system that can be displayed on the screen at one time. This number is limited by the circuitry of the display adapter, and is often much smaller than the number of colours the display device can actually support. The number of simultaneous colours a display adapter supports is normally determined by the number of colour planes, or bits per pixel, that it uses. For example, a device with 4 bits per pixel supports 16 simultaneous colors.