If a certain object does NOT reflect a certain frequency it is being applied the according "color" adjective.
660 nanometers is refered to as red. If an apple reflects all frequencies BUT this, then people say the apple 'is red'.
Violet light is electromagnetic radiation with wavelengths of 410 nanometers and red light has a wavelength of 680 nanometers.
Colors on PC audio connectors:
PC99 standard defines the following color codes to be used for PC soundcard connections:
* Pink: Microphone input * Green: Line/speaker/headphone output * Blue: Line in