Change the look of the media uploader

As starting point there is this action that allows inserting CSS and Javascript into the upload window.

add_action( 'admin_head-media-upload-popup', 'wpse_70750_style_upload_iframe' );

function wpse_70750_style_upload_iframe() 
{
    ?>
    <style type="text/css">
        #media-upload, #media-upload .media-item .slidetoggle { background-color:#555 }
    </style>
    <script type="text/javascript">
        jQuery(document).ready( function($) {
        });     
    </script>  
    <?php
}

Other Q&A’s that use this hook may be interesting.

Then, you may dig into the core file /wp-admin/includes/media.php and investigate all do_action and apply_filters that are available.