I know this question had already been solved, but I just want to chip in on my solution fwiw.
I had a problem of similar nature, with respect to .torrent files. Before, my default torrent client was utorrent, so naturally, all my .torrent files would show utorrent file icons. But I unistalled utorrent. Then i reinstalled utorrent. Upon reinstalling utorrent, however, I noticed that .torrent files are now showing blank icons in finder instead of the utorrent file icons i had before. That despite the fact that utorrent is now my only and default app for opening .torrent files.
So what I did is to clear my icon cache and that fixed my problem.
You can clear your icon cache by following these steps:
1. Close all active applications
2. Run terminal
3. Type the following command:
sudo rm -rf /Library/Caches/com.apple.iconservices.store
4. Terminal will prompt you for your admin password, so type that it and hit return
5. Reboot your mac
Good luck.