let coolor = 0;

let bg = 255;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(bg);

  fill(coolor);

  ellipse(200, 200, circleSize);

  circleSize = circleSize + 1;

  coolor = coolor + 1;

  bg = bg - 1;

}

​

function mousePressed() {

  circleSize = 1;

  coolor = 0;

  bg = 255;

}

​