Do you like Google's Favicon from 2012? That blue one with little contrast? No?
Then use the old one from 2009 which is colorful and easy to identify.
Want the old-school icon from 1998 instead? (first/original favicon)
Here you go: Google Favicon 1998
For Google Chrome:
Google Favicon 1998 - direct download
Google Favicon 2009 - direct download
By someone else: G Favicon Fixer - chrome store
This add-on was made to be small, fast and efficient, it uses as few resources as possible.
This is why every icon has it's own version (and small icon :P). If you want to change other sites icons as well, see:
Greasemonkey (when you use it anyway)
or any add-on dedicated to that job...