Trigger JS when featured image upload window is opened in admin

I’m trying to hook up some JS so that when the featured image upload box is opened and an image selected I can use Vibrant.js to analyse the colours of the selected image. The hurdle I’ve encountered is that I can’t find any particular event to bind my function to. I’ve looked at various tutorials regarding the wp.media() object, but they all seem to involve replacing the upload box completely. Is there no straightforward way of detecting when the featured image upload window is open and the selected thumbnail preview image is loaded?

How to manage attachment relationships for specific posts in WP 3.5+

In WordPress 3.5, media management has changed entirely. Also, relating attachments to specific posts is (I believe) basically only being done for backward compatibility. Therefore, after uploading attachments from within the media modal to a post of any post type, it establishes a relationship where the post ID is the parent of the attachment ID, like it’s been for a long time.