Every special occassion or theme day..
Google has changed their logo to fit in with the day..
be it a Uk or overseas festival or occasion.
On earth day i noticed how google had darkened their logo..
on April Fools day they had a fool them..
some of the logos are above.
Check back often by clicking Google search and let us see the logo that day..(Be sure to download the logo Do not copy and paste it)