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Using you 5050 RGB LED and looking at a data sheet the forward voltage drops are as follows Red is 2.2 Volts, Green is 3.2 Volts and Blue is also 3.2 Volts. With the 5050 LED it depends which manufacturer's data sheet you look at so the forward voltage drops Vf vary a little. Each color is 20 mA or 0.020 Amp. If you power all three LEDs on the chip with a forward current of 20 mA using correct series resistors you end up with White. Here is a color chart showing the color combinations. Personally I see no merit to using a RGB LED where a plane jane decent bright RED LED should be plenty visible in daylight under a soffit but your choice on that. You can go with a simple single LED as an indicator or have just about anything you want. The project can be very simple or more sophisticated depending on what you want. Going with a 5050 RGB LED running off 12 Volts you get for the Red 12 - 2.2 / .020 = 490 so a 510 Ohm series resistor for the red, Green and Blue 12 - 3.2 / .020 = 440 Ohms so a common 470 Ohm resistor. 1/4 watt resistors are fine.