Bi-colour LEDs light red when connected one way and green when connected the other.
Bi-color LED T1-3/4.
Red/Green LED - Only 2 leads. Very useful when prototyping you never have to remember if you have the LED the right way!
TIP: In our lab, we have a number of these LEDs lying around for development work. Trim one leg and solder a resistor (470 Ohm - 1K Ohm is fine) in it's place. You now have a handy LED circuit you can stick into a breadboard for testing and development of circuits.