Pins 1 to 16 are compatible with most 16x2 displays, where the last 2 are usually A (Anode +) and K (Cathode -). If you use only 16 pins, then you will use only the RED backlight. To fully use the 3-color LED, you need to add 2 more K (cathode) pins, for Green and Blue. I controlled them directly from the PWM outputs of an Arduino board. As the backlight is common anode, then each LED will lit 100% if AnalogWrite(pin, 0) is used, and be dark if AnalogWrite(pin, 255) is used. If the LEDs are driven following the manufacturer's recommendation, then use the following schematics and use the opposite values in AnalogWrite.