For 4 LEDs with a 3V forward voltage you would need a 1/2W 27 Ohm resistor, if you are using red LEDs then you would need a 33 Ohm resistor.
As has been said before you cannot mix LED colours in the circuit, as the different forward voltages will cause problems. If you want to power red, green and white LEDs you would need 3 separate circuits or add individual resistors to the LEDs.