r:0,

  g:0,

  b:0

}

​

function setup() {

  // This function runs only once

  createCanvas(400, 400);

  background(0);

}

​

function draw() {

  // This runs over and over again!

  col.r = map(mouseX, 0, 400, 0, 255);

  col.b = map(mouseY, 0, 400, 0, 255);

  fill(col.r, col.g, col.b);

  noStroke();

  circle(mouseX,mouseY,20);

}

​

function mousePressed(){

  background(0);

}