Hello,
to create the favicon images for my sites I use IcoMaker for Mac OS X 
. For this blog I only created the 16×16 and 32×32 icons, it seems that IcoMaker has a problem with 48×48 icons. I didn’t look deeper into it, but I think I used to many colors.
To add the favicon.ico to this site I followed the Creating a Favicon documentation on the WordPress Codex site.
The last step was to check the new favicon with the Favicon Validator .
Bye, Tore