RGB LED

RGB LEDs are actually just 3 LEDs (red, green, blue) that share one lens, and have one of their 2 pins in common (so 4 pins, one for each color, and one common). This common pin is either the anode (positive), or the cathode(ground) of each LED. With common cathode LEDs you connect the common pin to ground, and you supply power to the other pins to light them up. On a common anode LED you tie the common pin to power, and you bring the other pins down towards ground to power them. Many LED driver chips work exclusively with common anode LEDs, so know your application before you buy.

Different color LEDs require different voltage to power them, and an RGB LED is no different. Because it is actually 3 LEDs in one, the blue and green may max out at at 3.2v, the red may max out at 2.0v, so you can't even power them all the same. You need to check the doc sheet to know for sure.

The simplify things, you can always connect resistors to each of the 3 non-common legs to be able to power the red, blue and green with 5v.

Using these LEDs, all 3 colors have a current draw of 20ma. The blue and green are rated at 3.2v, and the red at 2.0v. So going over to the handy LED Calculator We find that a 100ohm resistor on both the green and blue pins, and a 150ohm resistor on the red pin will alow all 3 to operate at 5 volts (typical output on a Microcontroller).