int merah = 2;  
int kuning = 3; 
int k = 0;      

void setup() {
  pinMode(merah, OUTPUT);  
  pinMode(kuning, OUTPUT); 
}

void loop() {
  for (k = 0; k < 255; k++) {
    analogWrite(merah, k);  
    analogWrite(kuning, 255 - k);  
    delay(10);  
  }
  
  if (k == 255) {
    k = 0; 
  }

  for (k = 0; k < 255; k++) {
    analogWrite(kuning, k);  
    analogWrite(merah, 255 - k);  
    delay(10);  
  }
  
  if (k == 255) {
    k = 0; 
  }
}