You will now find that you can theme your AdSense ad units using a new feature introduced by AdSense. To take advantage of the new themes go to My Account > Ad Type Preference and enable the check box for themed units.
Themed units are not permanent, they will only when appropriate, eg. Christmas, 4th July, Thanksgiving etc.
As part of our ongoing effort to provide ad designs that will improve results for both advertisers and publishers, we now offer themed ad units; ad units that display themed colours and graphics during holidays and special events. You can view examples of themed ad units by visiting our Ad Formats page.
Whenever themed ad units are available, we will display them only to users in the appropriate locations, as determined by user IP address. For example, Fourth of July-themed ads would be visible only to users located in the U.S. while users throughout the world might see ads with a New Year’s Eve theme.
It’ll be interesting to see how CTR is affected as these themes will certainly draw attention to the ads.