LED stands for Light Emitting Diode. It is a semiconductor that emits light when you send a certain electric current through it. The colour of the LED does not depend on the housing, but on the type of material of which the conductor is made.

As a comparison: an incandescent lamp bulb emits light because a filament is heated. This immediately shows one of the major differences with a LED. It does not lose any energy to heat and is therefore much more efficient.