Others have four legs, which makes sense to me, as ground can be shared.
One of many examples of a six legged RGB LED is the Kingbright KAF-5060PBESEEVGC.
Electronic – Why do some RGB LEDs have six legs
ledrgb
Related Solutions
Have a look at the LED truth table on the same page:
Each output is consecutively active for the same time. By wired-OR-ing outputs you can create longer active times. So the green LED will be on during 4 time units.
Normally you would have to wired-OR Q0 through Q4 for the red LED, but we have a carry output (here called ":10") which does just that, see the bottom trace of the timing diagram:
I can see two ways of achieving this.
1-Using a technique called Charlieplexing to control your leds. With 10 output pins you would be able to control 90 normal leds. The main disadvantage with this technique is that the leds are not always on. They flash really fast, causing a reduction in the brightness of the leds. It's also a bit complicated to code and I'm not 100% certain that you could make it work on RGB leds.
2-Using Shift registers. Like this one. With shift registers you can ouput data in a serial fashion and output it in parallel. Depending on the number of pins you are willing to use, you'll have to buy more or less Shift registers. The main idea is something like: output the new states of the leds, one by one (separating your signals by outputting HIGH to the SRCLK) and then "applying changes" by outputing HIGH to RCLK. If you think about it, you can basically cascade to an infinite number of outputs. You'll need a lot of shift registers though and the response time will probably be slow.
Best Answer
According to the datasheet, it has six legs because it contains 3 LEDs, with nothing common:
Many RGB LEDs have a common cathode or common anode, so need only 4 leads. For some applications that may not be acceptable. For example, it wouldn't be possible to control two RGB LEDs with common cathodes or anodes in series, or to arrange them for charlieplexing.
Further, a part like this is at least more flexible. It can be made common anode, or common cathode. Or, a pair of the LEDs may be arranged in anti-parallel. It may make more sense in some situations to stock just one part than to stock several different parts to cover different cases.