#define RED_PIN D4
#define GREEN_PIN D5
#define BLUE_PIN D0

void setup() {
  Serial.begin(115200);
  pinMode(D4, OUTPUT);
  pinMode(D5, OUTPUT);
  pinMode(D0, OUTPUT);
}

void loop() {
  if (Serial.available()) {
    char c = Serial.read();
    
    switch(c) {
      case 'r': digitalWrite(RED_PIN, HIGH); break;
      case 'g': digitalWrite(GREEN_PIN, HIGH); break;
      case 'b': digitalWrite(BLUE_PIN, HIGH); break;

      case 'R': digitalWrite(RED_PIN, LOW); break;
      case 'G': digitalWrite(GREEN_PIN, LOW); break;
      case 'B': digitalWrite(BLUE_PIN, LOW); break;
    }
  }
}