How to change backlight color of 2x16 LCD display

Question

I am using 2x16 LCD display with 16 header pins with Raspberry Pi 3 .To display messages I installed and configured Adafruit Char LCD library. and it works fine.

currently default backlight color is yellow, so I want to change it to other colors like blue, red . for this ,I imported Adafruit_RGBCharLCD class Adafruit_RGBCharLCD from Adafruit char LCD library is as follows

class Adafruit_RGBCharLCD(Adafruit_CharLCD):
    """Class to represent and interact with an HD44780 character LCD display with
    an RGB backlight."""

    def __init__(self, rs, en, d4, d5, d6, d7, cols, lines, red, green, blue,
                 gpio=GPIO.get_platform_gpio(), 
                 invert_polarity=True,
                 enable_pwm=False,
                 pwm=PWM.get_platform_pwm(),
                 initial_color=(1.0, 1.0, 1.0)):
        """Initialize the LCD with RGB backlight.  RS, EN, and D4...D7 parameters 
        should be the pins connected to the LCD RS, clock enable, and data line 
        4 through 7 connections. The LCD will be used in its 4-bit mode so these 
        6 lines are the only ones required to use the LCD.  You must also pass in
        the number of columns and lines on the LCD.

        The red, green, and blue parameters define the pins which are connected
        to the appropriate backlight LEDs.  The invert_polarity parameter is a
        boolean that controls if the LEDs are on with a LOW or HIGH signal.  By
        default invert_polarity is True, i.e. the backlight LEDs are on with a
        low signal.  If you want to enable PWM on the backlight LEDs (for finer
        control of colors) and the hardware supports PWM on the provided pins,
        set enable_pwm to True.  Finally you can set an explicit initial backlight
        color with the initial_color parameter.  The default initial color is
        white (all LEDs lit).

        You can optionally pass in an explicit GPIO class,
        for example if you want to use an MCP230xx GPIO extender.  If you don't
        pass in an GPIO instance, the default GPIO for the running platform will
        be used.
        """
        super(Adafruit_RGBCharLCD, self).__init__(rs, en, d4, d5, d6, d7,
                                                  cols,
                                                  lines, 
                                                  enable_pwm=enable_pwm,
                                                  backlight=None,
                                                  invert_polarity=invert_polarity,
                                                  gpio=gpio, 
                                                  pwm=pwm)
        self._red = red
        self._green = green
        self._blue = blue
        # Setup backlight pins.
        if enable_pwm:
            # Determine initial backlight duty cycles.
            rdc, gdc, bdc = self._rgb_to_duty_cycle(initial_color)
            pwm.start(red, rdc)
            pwm.start(green, gdc)
            pwm.start(blue, bdc)
        else:
            gpio.setup(red, GPIO.OUT)
            gpio.setup(green, GPIO.OUT)
            gpio.setup(blue, GPIO.OUT)
            self._gpio.output_pins(self._rgb_to_pins(initial_color))

    def _rgb_to_duty_cycle(self, rgb):
        # Convert tuple of RGB 0-1 values to tuple of duty cycles (0-100).
        red, green, blue = rgb
        # Clamp colors between 0.0 and 1.0
        red = max(0.0, min(1.0, red))
        green = max(0.0, min(1.0, green))
        blue = max(0.0, min(1.0, blue))
        return (self._pwm_duty_cycle(red), 
                self._pwm_duty_cycle(green),
                self._pwm_duty_cycle(blue))

    def _rgb_to_pins(self, rgb):
        # Convert tuple of RGB 0-1 values to dict of pin values.
        red, green, blue = rgb
        return { self._red:   self._blpol if red else not self._blpol,
                 self._green: self._blpol if green else not self._blpol,
                 self._blue:  self._blpol if blue else not self._blpol }

    def set_color(self, red, green, blue):
        """Set backlight color to provided red, green, and blue values.  If PWM
        is enabled then color components can be values from 0.0 to 1.0, otherwise
        components should be zero for off and non-zero for on.
        """
        if self._pwm_enabled:
            # Set duty cycle of PWM pins.
            rdc, gdc, bdc = self._rgb_to_duty_cycle((red, green, blue))
            self._pwm.set_duty_cycle(self._red, rdc)
            self._pwm.set_duty_cycle(self._green, gdc)
            self._pwm.set_duty_cycle(self._blue, bdc)
        else:
            # Set appropriate backlight pins based on polarity and enabled colors.
            self._gpio.output_pins({self._red:   self._blpol if red else not self._blpol,
                                    self._green: self._blpol if green else not self._blpol,
                                    self._blue:  self._blpol if blue else not self._blpol })

    def set_backlight(self, backlight):
        """Enable or disable the backlight.  If PWM is not enabled (default), a
        non-zero backlight value will turn on the backlight and a zero value will
        turn it off.  If PWM is enabled, backlight can be any value from 0.0 to
        1.0, with 1.0 being full intensity backlight.  On an RGB display this
        function will set the backlight to all white.
        """
        self.set_color(backlight, backlight, backlight)

and I am trying to used lcd.set_color() as follows , but its not working.

import time
from Adafruit_CharLCD import Adafruit_RGBCharLCD

# instantiate lcd and specify pins
lcd = Adafruit_RGBCharLCD(rs=26, en=19,
                       d4=13, d5=6, d6=5, d7=11,
                       cols=16, lines=2,red=True,Green=True,Blue=True)
lcd.clear()
#setting backlight color as blue
lcd.set_color(0,0,100)


# display text on LCD display \n = new line
lcd.message('2x16 CharLCD\n  Raspberry Pi')

I am using 4 bit node,attached last two pins which are backlight pins to raspberry pi gpio pins as follows:

Backlight Pins

  15     LED+ or A        Pin No 2 of GPIO(5v Power)
  16      LED- or K       Pin No 6 of GPIO(GND)

please help me to set customized colors as backlight ,as I am new to all this.

Answer 1

If your display has pins for backlight (LED) you can switch the backlight ON and OFF only unless there is some voltage regulation available, which I doubt. Usually displays based on HD44780 chip do not support backlight color change. You can only switch it ON and OFF.