createCanvas(200, 200);

  // Align text center both horizontally and vertically.

  textAlign(CENTER, CENTER);

  textSize(50);

}

​

function draw(){

  // Calculate a colour for the background based on frameCount.

  // Use the modulo operator to 'wrap around' at 255.

  let bgColour = frameCount % 255;

  background(bgColour);

  // Calculate a fill opposite to cbackground.

  let fillColour = 255 - bgColour;

  fill(fillColour);

  // Draw the frameCount at the center of the canvas. 

  text(frameCount, width / 2, height / 2);

}