createCanvas(400, 400);

  colorMode(HSB);

  noStroke();

}

​

function draw() {

  background(220);

  let leftHue = map(mouseX, 0, width, 0, 360);

  fill(leftHue, 100, 100);

  rect(0, 0, width/4, height);

  for (let i = 1; i < 4; i +=1) {

    fill((leftHue + i*30)%360, 100, 100);

    rect(width/4*i, 0, width/2, height);

  }

}