createCanvas(720, 720);

    colorMode(HSB, 360, 100, 100); 

    rectMode(CENTER);

    noCursor();

    noStroke();

}

​

function draw() {

  background(mouseY / 2, 200, 50);

  fill(360 - mouseY / 2, 100, 100); 

  rect(mouseX, mouseY, mouseX, mouseY);   

}