int Yellow=8;
int Red=9;
int Green=10;
int Blue=11;
void setup() {
     Serial.begin(9600);
  // put your setup code here, to run once:
pinMode(Yellow,OUTPUT);
pinMode(Red,OUTPUT);
pinMode(Green,OUTPUT);
pinMode(Blue,OUTPUT);

}

void loop() {

   if (Serial.available()) {  // Check if data is received
        char command = Serial.read();  // Read the command
        Serial.println(command);  // Print command for debugging

        switch (command) {
            case 'Y':  
    digitalWrite(Yellow,HIGH);
   break; 
              case 'R':  
  digitalWrite(Red,HIGH);
  break;
              case 'G':  
    digitalWrite(Green,HIGH);
   break; 
              case 'B':  
  digitalWrite(Blue,HIGH);
  break;
  case 'O':  
  digitalWrite(Yellow,LOW);
  digitalWrite(Red,LOW);
  digitalWrite(Green,LOW);
  digitalWrite(Blue,LOW);  break;
    case 'A':  
  digitalWrite(Yellow,HIGH);
  digitalWrite(Red,HIGH);
  digitalWrite(Green,HIGH);
  digitalWrite(Blue,HIGH);  break;
  // put your main code here, to run repeatedly:

        }
        }
        }