SOURCE

function setup() {
	createCanvas(500,500);
	background(250);
  
}

function draw() {
	for (var y=0;y<height; y +=50) {
		for (var x= 0;x<=width;x+=50) {
			fill(160,280,360);
			rect(x,y,50,50);
		}
	}
    for (var y=0;y<height; y +=50) {
		for (var x= 0;x<=width;x+=50) {
			fill(60,360,90);
			rect(x+5,y+5,40,40);
		}
	}
    for (var y=0;y<height; y +=50) {
		for (var x= 0;x<=width;x+=50) {
			fill(360,360,360);
			rect(x+10,y+10,30,30);
		}
	}
    for (var y=0;y<height; y +=50) {
		for (var x= 0;x<=width;x+=50) {
			fill(360,60,360);
			rect(x+15,y+15,20,20);
		}
	}

  
}

 <script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script>