A simplified version of the example sketch that comes with the RGBLED library

rgbled_simplified.ino

#include "RGBLED.hpp"

// Pin mapping for the first RGBLED object:
const byte redLed = 3;
const byte greenLed = 5;
const byte blueLed = 6;
// The RGBLED object defaults to common cathode configuration.
RGBLED rgbLed(redLed, greenLed, blueLed);

void setup() {
  Serial.begin(250000);
  Serial.println("RGBLED 'hello_world' example.");
  rgbLed.brightness(PWM_MAX); // Sets the brightness.
}

void loop() {
  // Turns ON the led.
  rgbLed.on();

  // Sets PWM for a color. Get these numbers from the Google Color chooser.
  rgbLed.red(115); rgbLed.green(183); rgbLed.blue(150);
  
  // The method 'RGBLED::show()' must be called to execute the changes.
  rgbLed.show();

  delay(1000);  // Keep this color for 1 second

  // Turns OFF the led. This must be done so that we can change the color
  rgbLed.off();

  // Turns ON the led.
  rgbLed.on();


  // Sets PWM for a color. Get these numbers from the Google Color chooser.
  rgbLed.red(183); rgbLed.green(115); rgbLed.blue(146);
  // The method 'RGBLED::show()' must be called to execute the changes.
  rgbLed.show();

  delay(1000);

  // Turns OFF the led. This must be done so that we can change the color
  rgbLed.off(); 
}