If you picked a background image for Google's homepage, you probably noticed that Google uses a special white logo. Unfortunately, the customized homepage can't show the regular Google logo and Google doodles for special events.
That's the reason why Google shows a small notification icon next to the logo when there's a doodles you can't see.
When you click on the colorful icon, Google shows the doodle on a white background.
I wonder if Google will use full-page doodles for users who picked a background image.