int greenpin=13;
int yellowpin=12;
int whitepin=11;
String mycolour;
String msg="what colour do you want?";
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
pinMode(greenpin, OUTPUT);
pinMode(yellowpin, OUTPUT);
pinMode(whitepin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
Serial.println(msg);
while (Serial.available()==0) {

}
mycolour=Serial.readString();

if (mycolour=="red") {
digitalWrite(greenpin,HIGH);
digitalWrite(yellowpin,LOW);
digitalWrite(whitepin,LOW);
}

if (mycolour=="yellow") {
digitalWrite(greenpin,LOW);
digitalWrite(yellowpin,HIGH);
digitalWrite(whitepin,LOW);
}
if (mycolour=="white") {
digitalWrite(greenpin,LOW);
digitalWrite(yellowpin,LOW);
digitalWrite(whitepin,HIGH);
}

}