My set_scene.js
function set_scene(n) {
  var scene=document.getElementById('scene');
  scene.src='images/scenes/'+n+'.jpg';
  Hide_class('item');
  if (n==3) Show('blue');
  if (n==16) Show('green');
}

Here's two more to add to your work - scene numbers 15 & 7 (indigo).