I'm pretty sure it's one of these one-day pranks google loves to do, like the pacman "logo", just a bit more intrusive and annoying then usual. Well, I hope so at least...
It can't possibly not be, if you'll pardon the double negative. There's no way they'd switch to white "Google" text after so many years' investment in the bright colours.
(Yes, I know Apple removed its colours, but that's different.)
