A two-colour LED consists of two light-emit- ting diodes, usually red and green, encapsu- lated in the same case. It has three pins: two for the anodes, and one for the common cathode. In this way, each diode can be activated separately. Various colours may be obtained by varying the current through one or both of the diodes. For example, four colours may be obtained when the currents. are arranged as follows: red, green, orange R 21G) and yellow (IG-21R). This Multi Color Led Circuit is very easy to build at home.