AdWords ads appearing above search results on Google.com now have a new look, according to the Inside AdWords blog. The sponsored links that appear above organic search results will now have a yellow background, instead of the previous blue background.
To lessen unintentional clicks on ads, Google has also changed the way it processes clicks on those ads, from allowing a click anywhere in the box to count as a click to requiring the user to click on the link in the top line, as in other ads.
Google has been testing the changes for a few weeks now. The moves are expected to lower clickthrough rates, but should improve ROI, as users that do click through are more likely to have done so intentionally.