createCanvas(400, 400);

  background(0);

}

​

function draw() {

  rectMode(CENTER)

  fill(0,mouseY,mouseX)

  rect(mouseX,mouseY,mouseY,mouseX)

  fill(mouseX,mouseY,0)

  circle(mouseX,mouseY,100)

  fill(mouseY,mouseX,0)

  circle(mouseX,mouseY,70)

}