Recently the favicon for Google Reader has been updated.
The new icon has more colors, and looks definitely better.
In case that you still see the old one, due to your browser’s cache, here’s what you can do:
1. Navigate to http://www.google.com/reader/ui/favicon.ico
2. Press shift on your keyboard and click on Refresh/Reload on your browser to get the new icon.
This is it, enjoy the new favicon!