#define PinR  11
#define PinG  10
#define PinB  9
char caracter;

void setup() {
  Serial.begin(9600);
  pinMode(PinR, OUTPUT);
  pinMode(PinG, OUTPUT);
  pinMode(PinB, OUTPUT);
  analogWrite(PinR, 0);
  analogWrite(PinG, 255);
  digitalWrite(PinB, LOW);
}

void loop() {
  if (Serial.available()) {
    caracter = Serial.read();

    if (caracter == 'a')
    { analogWrite(PinR, 255);
      analogWrite(PinG, 255);
      digitalWrite(PinB, HIGH);
    }
    if (caracter == 'b')
    { analogWrite(PinR, 0);
      analogWrite(PinG, 255);
      digitalWrite(PinB, HIGH);
    }
    if (caracter == 'c')
    { analogWrite(PinR, 255);
      analogWrite(PinG, 0);
      digitalWrite(PinB, HIGH);
    }
    if (caracter == 'd')
    { analogWrite(PinR, 0);
      analogWrite(PinG, 0);
      digitalWrite(PinB, LOW);
    }
  }
}