​

function setup() {

  createCanvas(400, 400);

  colorMode(HSB, 360, 100, 100, 100);

}

​

function draw() {

  background(200, 10, 90);

  // Draw a circle in the centre of the canvas, 

  // using a variable for hue

  fill(h, 100, 100);

  ellipse(200, 200, 100);

}

​

// When the mouse is clicked, turn the hue to blue 

function mouseClicked(){

  h = 250;

}

​

​