int redPin=9;
int yellowPin=6;
int buttPin=2;

volatile int buttonstate;

void buttonpress() {  
  buttonstate=digitalRead(buttPin);

  if (buttonstate==HIGH)

     {digitalWrite(yellowPin,HIGH);} 
  else
     {digitalWrite(yellowPin,LOW);}}

void setup() {

pinMode(redPin, OUTPUT);
pinMode(yellowPin, OUTPUT);
pinMode(buttPin, INPUT);

attachInterrupt(digitalPinToInterrupt(buttPin),buttonpress, CHANGE);

}

void loop() {

digitalWrite(redPin,HIGH);
delay(250);
digitalWrite(redPin,LOW);
delay(250);

}