var on = false;

​

function setup() {

  createCanvas(600, 400);

  // Starting location

  x = 300;

  y = 200;

  // Dimensions

  w = 100;

  h = 100;

}

​

function draw() {

  if(on){

    background(0,0,255);

  }else {

    background(0);

  }

  stroke(225);

  strokeWeight(4);

  noFill();

    //rollover-rect changes color when mouse is inside

  if(mouseX > 250 && mouseX < 350 &&mouseY >150 && mouseY < 250){

    fill(0,0,255);

  }

​

  rectMode(CENTER)

  rect(x,y,w,h);

}

   //when mouse is pressed, set the backgrounds blue,red, green.

  function mousePressed(){

    if(mouseX > 250 && mouseX < 350 &&mouseY >150 && mouseY < 250)

    on=!on;

  fill(255,0,0);

  rectMode(CENTER)

  rect(x,y,w,h);

}

​

​

​