String msg="das";

void setup() {
  Serial.begin(9600);
  Serial.print("vitaj");
  pinMode(7, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(5, OUTPUT);
  
  

}

void loop() {
  if(Serial.available())
  {
    msg=Serial.readStringUntil('\n');
    Serial.print(msg);

    while(Serial.available())
      Serial.read();

    if(msg == "cervena")
    {
      digitalWrite(7, HIGH);
      digitalWrite(6, LOW);
      digitalWrite(5, LOW);
    }

    if(msg == "zelena")
    {
      digitalWrite(7, LOW);
      digitalWrite(6, HIGH);
      digitalWrite(5, LOW);
    }

    if(msg == "modra")
    {
      digitalWrite(7, LOW);
      digitalWrite(6, LOW);
      digitalWrite(5, HIGH);
    }

    if(msg == "vypnut")
    {
      digitalWrite(7, LOW);
      digitalWrite(6, LOW);
      digitalWrite(5, LOW);
    }
  }

}