int red = 13;
int green = 12;
int blue = 8;

void setup(){
  pinMode(red, OUTPUT);
  pinMode(green, OUTPUT);
  pinMode(blue, OUTPUT);
}

void loop(){
  digitalWrite(red, HIGH);
  digitalWrite(green, LOW);
  digitalWrite(blue, LOW);
  delay(3000);
  digitalWrite(red, LOW);
  digitalWrite(green, HIGH);
  delay(3000);
  digitalWrite(green, LOW);
  digitalWrite(blue, HIGH);
  delay(3000);
}