LED_RGB.ino

const unsigned char LED_RED = 3;
const unsigned char LED_GREEN = 5;
const unsigned char LED_BLUE = 6;

void setup() {
  Serial.begin(9600);
  pinMode(LED_GREEN, OUTPUT);
  pinMode(LED_BLUE, OUTPUT);
  pinMode(LED_RED, OUTPUT);
}

void loop() {
  char leds[] = {LED_RED, LED_GREEN, LED_BLUE};
  int i;
  for(const char &led : leds) {
    for (i = 0; i < 255; i = i + 1) {
      analogWrite(led, i); 
      delay(10);
    }
  }
  for(const char &led : leds) {
    for (i = 255; i >= 0; i = i - 1) {
      analogWrite(led, i); 
      delay(10);
    }
  }
}