createCanvas(200, 200);

​

  // Align text center both horizontally and vertically.

  textAlign(CENTER, CENTER);

  textSize(50);

}

​

function draw(){

  // Store the current milliseconds in variable 'ms'.

  // We use floor to get rid of the decimal places. 

  let ms = floor(millis());

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

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

  // Dividing ms by 10 slows the speed of change down.

  let bgColour = (ms / 100) % 255;

  background(bgColour);

​

  // Calculate a fill opposite to the background.

  let fillColour = 255 - bgColour;

  fill(fillColour);

​

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

  text(ms, width / 2, height / 2);

}