The resistor colour code (or electronic colour code), is a system of colours used to indicate the first 10 integers 0-9; it is primarily used to label resistors and capacitors, and in audio we use the colours and their respective numbers to label cables and connections.

The colours are as follows:

The most common places this is found in audio is to identify the channels on a multicore (snake) or loom cable, or inside fixed installations to identify connections between rack mounted units.

You can read more about it here.