function setup() {
  createCanvas(160, 160);
}

function tekenPixels(pixels) {
  for(var i = 0; i < pixels.length; i++) {
    for(var j = 0; j < 4; j++) {
      var color = pixels[i][j];
      fill(color);
      strokeWeight(0);
      rect(j*40, i*40, 40, 40);
    }
  }
}

function draw() {
  background(220);
 
  var pixels = [
    [255,255,255,255],
    [0,100,0,100],
    [255,255,255,255],
    [0,50,0,150]
  ];
 
  tekenPixels(pixels);
}