Over 3 years back, Google switched from blue to yellow background of Google AdWords ads, with a change to how on-click events occur. "Google has now begun rolling out a new "pale purple" background for AdWords listings on Google's search results."
Google said "Starting today and ramping up to 100% globally by the end of this week, we'll be changing the background color for ads that appear above the search results on Google.com as well as our local domains. The ads, which currently have a pale yellow background, will change to have a pale purple background. This change is part of the "look and feel" update to our color palette and logo that we made back in May of this year to keep the Google results page looking fresh and modern. This's purely an aesthetic change to our ads and won't have any impact on the way we target or serve advertisements on Google.com."