#define red 7
 #define blue 6

void setup() {
pinMode(red, OUTPUT);
pinMode(blue, OUTPUT);
Serial.begin(9600);
}

void loop() {

digitalWrite(red, HIGH);
Serial.println("cervena");
delay(500);
digitalWrite(red, LOW);

digitalWrite(blue, HIGH);
Serial.println("modra");
delay(500);
digitalWrite(blue, LOW);
}