createCanvas(400, 400);

}

​

function draw() {

  let brightness = map(mouseX, 0, width, 0, 255);

  let r = map(mouseX, 0, width, 0, 255);

  let g = map(mouseY, 0, height, 0, 255);

  let b = map(mouseY, 0, height, 0, 255);

  background(brightness);

  rectMode(CENTER);

  //fill(255-brightness);

  fill(r, g, b);

  rect(width/1.5,height/1.5,100, 100);

  rect(width/2,height/2,100, 100);

  rect(width/6,height/6,100, 100);

  rect(width/5,height/5,100, 100);

}