It looks like Google is testing out different colors for sponsored search results. I noticed this today – the sponsored section on the first SERP is a pinkish-peach color in the background, which is how it always has been. But the same section on the 2nd SERP is a blueish color. Looks like Google is testing CTR with different background colors.
What does this mean for SEO? Well, Google is always testing out little details like this and trying to optimize for better results, both for its advertisers and its users. Considering the amount of traffic Google sees every day, even a tiny improvement could be worth a huge heap of money to them in the long run. So they carefully test these things out and make changes according to their test results. This could result in better CTR for our AdWords accounts, which is always a good thing.