​

function setup() {

  createCanvas(100, 100);

}

​

function draw() {

  background(200);

  fill(value);

  square(25, 25, 50);

}

​

// Trigger when touch starts

function touchStarted() {

  toggleColor()

}

​

// Trigger when mouse is pressed (for desktop)

function mousePressed() {

  touchStarted()

}

​

function toggleColor() {

  if (value === 0) {

    value = 255;

  } else {

    value = 0;

  }

}