Google personalized homepage has supported theme. Just now I found this news on cnbeta. It is an interesting new feature. Google always gives us much surprise. But this feature is only for english users. If you wanna use this function, you should change your google homepage to english language at first. Then, click the "select theme" button and choose the theme you like. I chose "Seasonal Scape", and it asked me the city I live in. It seems that the theme will change as the time goes by.

Here is a picture of my google theme.

-----------update------------

The theme has changed. It's cool!