createCanvas(600, 600);

  colorMode(RGB, 255);

}

​

function draw() {

  background(255);

  for(var x = 30; x <= 600; x += 30) {

    var c = map(x, 30, 600, 0, 1);

    let black = color(0);

    let white = color(255);

    fill(lerpColor(black, white, c));

    rect(x - 30, height - x, 30, x);

  }

}