problem in running a RGB Led with pyfirmata

[msarvi]

I decided to run RGB led with python Pyfirmata, I read documents, and use the following script:

import pyfirmata
import time
arduino =pyfirmata.Arduino('/dev/cu.usbmodem1411', baudrate=9600)

arduino.digital[9].mode = pyfirmata.OUTPUT
arduino.digital[10].mode = pyfirmata.OUTPUT
arduino.digital[11].mode = pyfirmata.OUTPUT
while True:
    arduino.digital[9].write(0.56)
    arduino.digital[10].write(0.76)
    arduino.digital[11].write(0.67)
    time.sleep(5)

arduino.exit()

no error or exceptions occurred, but the led is not turned on. even I changed the pin modes to PWM.