String msg1 = "what color of led do you want to blink";
int greenpin=9;
int yellowpin = 10;
int redpin = 11;
String mycolor;
void setup() {
  Serial.begin(9600);
  pinMode(redpin, OUTPUT);
  pinMode(yellowpin, OUTPUT);
  pinMode(greenpin, OUTPUT);
 
}

void loop() {
  Serial.println(msg1);
  while(Serial.available()==0)
  {

  }
  mycolor=Serial.readString();
if(mycolor=="red")
{
digitalWrite(redpin, HIGH);
digitalWrite(greenpin, LOW);
digitalWrite(yellowpin, LOW);

  }
  if(mycolor=="yellow")
  {
    digitalWrite(redpin, LOW);
digitalWrite(greenpin, LOW);
digitalWrite(yellowpin, HIGH);

  }
  if(mycolor=="green")
  {
    digitalWrite(redpin, LOW);
digitalWrite(greenpin, HIGH);
digitalWrite(yellowpin, LOW);

  }
}