You make it sound so easy, and it was under breezy, but it hasn't under edgy.

I'm trying to associate an icon, gnome-mime-video-ty.png, with tystreams. I've edited /usr/share/mime/packages/ to include:

<mime-type type="video/ty">
<comment>Tivo transport stream</comment>
<glob pattern="*.ty"/>

Executed: sudo update-mime-database /usr/share/mime

Sure enough, nautilus describes Doctor Who-Rose.ty as:

Type: Tivo transport stream
MIME type: video/ty

I put my icon in ~/.icons/Nuovo/24x24/mimetypes as gnome-mime-video-ty.png, and in gnome-theme-manager->Theme Details->Icons I selected Dropline Nuovo, noticing when I did that the folder icons in nautilus changed to the distinctive yellow icons. (Note: Dropline Nuovo "Inherits=gnome".)

The icon associated with *.ty files is, however, the gnome one that looks like /usr/share/icons/gnome/32x32/mimetypes/video-x-generic.png, to which gnome-mime-video.png is symlinked. It is the same icon associated with Doctor Who-Rose.ty.vob, described in nautilus as:

Type: MPEG video
MIME type: video/mpeg

What do I have to name my icon to get nautilus to use it for tystreams?