Google's home page sports a colorful -- but mysterious -- new interactive logo this morning.

The logo, apparently visible only to browsers in the United States and Britain (UPDATE: A number of readers in France say they can see the logo, though at least one says he can't. Availability outside the US/UK sounds spotty) shows the word 'Google' made up colorful circles that scatter around your screen when you mouse over them. It's neat, but what is it doing there?

Usually Google's custom logos are tied to holidays or historical events in a way that is fairly obvious, and, when users are confused, clicking on the logo triggers a search explaining it. This time, however, clicking on the logo does nothing.

There is already a lot of speculation out there, for instance that this has something to do with Google's birthday. But Google denies this, and none of the other explanations we've read seem convincing.

What do our readers think?

If you haven't seen it, here it is: