void setup() {
  Serial.begin(115200);
  Serial.println("Hello, ESP32!");
  pinMode(19, OUTPUT);
  pinMode(18, OUTPUT);
  pinMode(5, OUTPUT);
}

void loop() {
  if (Serial.available()) {
    char color = Serial.read();
    if (color == 'r') {
      digitalWrite(19, LOW);
      digitalWrite(18, HIGH);
      digitalWrite(5, HIGH);
    }
    else if (color == 'g') {
      digitalWrite(19, HIGH);
      digitalWrite(18, LOW);
      digitalWrite(5, HIGH);
    }
    else if (color == 'b')  {
      digitalWrite(19, HIGH);
      digitalWrite(18, HIGH);
      digitalWrite(5, LOW);
    }
  }
}