For the past few months, Google is constantly flipping the background colors for the Sponsored Links section in the SERP that feature ads.
In the month of May 2010, you would have noticed continuous updates in Search Engine Roundtable blog on changing the ads background. It was also reported on 2008 that Google Testing Green Backgrounds & Turns Directory Ads Green followed by Google Testing Pink Background For AdWords Ads in 2010.
Now from changing the Google Directory Ads from Green they have started testing it in SERP. You can find the details on the colors that they have been working around below,
Post your views in the comment section on the color that you feel will be ideal to replace the existing color Pale Yellow or your thoughts on flipping it.