making the blue shape work:

Change one line in index.html:

    <img src='images/shapes/blue.png' id='blue' class='item' onClick='shape_clicked(this);'>

Add this to globals.js:

var g_blue=true;

Change one line in set_scene:

  if (n==3 && g_blue) Show('blue');

shape_clicked function

function shape_clicked(image) {
  var id=image.id;
  Hide(id);
  if (id=='blue') g_blue=false;
}

Now add the other 6 shapes in the same way.

Finally! The Rainbow!

My idea is that as each coloured shape is "picked up", that part of the rainbow will show up on scene 1.
Note that you can't use, for example, red for the id of the red arch as we've used it already for the red shape.
I suggest just using the first letter, r.
And each image should be put in the rainbow class because all share the same grid location: 1 / 5; 1 / 8;