const int redPin   = 3;        
const int greenPin = 5;
const int bluePin  = 6;

int R, G, B;  
int error = 0;

void setup()
{
  // Par défaut, donc facultatif...
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
  pinMode(13, OUTPUT);
  R = 0;
  G = 255;
  B = 0;
  Serial.begin(9600);
  analogWrite(redPin, 255-R);
  analogWrite(greenPin, 255-G);
  analogWrite(bluePin, 255-B );
  
}

void loop()
{
  char commande;
  
  if (Serial.available()) {
    commande = Serial.read();
    if (commande == 'L') {
      R = Serial.read();
      G = Serial.read();
      B = Serial.read();
      analogWrite(redPin, 255-R);
      analogWrite(greenPin, 255-G);
      analogWrite(bluePin, 255-B );
      error = 0;
    }
    else {
      error = 1;
    }
  }

  if (error) digitalWrite(13, HIGH);
  else digitalWrite(13, LOW);

  delay(100);
}