RGB LEDs

Dada, RGB Piranha 5mm is what I got.

RGB LEDs producing different colours in one application

Longest lead (pin 2) is Cathode (-)

Pin 1 -( emits light of 650nm) Green - Short Lead (same length as Green)
Pin 2 - Negative/Cathode Longest lead
Pin 3 - CB (emits light of 470nm) - Blue - 2nd longest lead
Pin 4 - BG (emits light of 520nm) - Red - Short lead (same length as red)

Pin 2 (longest) is the common cathode to all 3 colors.

Read more: http://www.divilabs.com/2013/04/multi-color-leds-beginner-level-guide.html#ixzz2yINjX5cl