Daniel Dulitz, Product Manager for the Google.com ads announced — “We've now made two changes to the way that we display these ads to improve the experience of our users and advertisers.”
After months of testing, we decided to switch the background color of the top ads from blue to yellow. Second, we've modified what counts as a click in this box to be consistent with what counts as a click for the ads on the right hand side. Instead of clicking anywhere in the box, users now need to click on the link in the top line of an ad in order to be taken to an advertiser's site. Together, these changes help decrease the likelihood that a user will unintentionally click on an ad, while making our highest quality ads more visible.
Source:→ AdWords BlogGoogle, AdWords, Ads