int led_red= 2;
int led_green= 4;
int led_blue= 6;

void setup (){
  Serial.begin(115200);
  Serial.print("t");
  pinMode(led_red, OUTPUT);
  pinMode(led_green, OUTPUT);
  pinMode(led_blue, OUTPUT);
}

void loop(){
  if (Serial.available()){
    String state = Serial.readString();
    state.trim();

    if (state == "red"){
      digitalWrite(led_red, HIGH);
      digitalWrite(led_green, LOW);
      digitalWrite(led_blue, LOW);
    }
  
    if (state == "green"){
      digitalWrite(led_green, HIGH);
      digitalWrite(led_red, LOW);
      digitalWrite(led_blue, LOW);
    }
  
    if (state == "blue"){
      digitalWrite(led_blue, HIGH);
      digitalWrite(led_red, LOW);
      digitalWrite(led_green, LOW);

    }
  }
}