From time to time I see reports of people saying the Google AdWords ad background color has changed from the yellow to a different color.
Today, I spotted a thread at Google Web Search Help of a person noticing pink backgrounds for the AdWords location. Here is a picture he posted in the thread:
This is compared to what most people see, the yellow background:
We spotted pink background back in May and we have seen Google move from the old blue background to the yellow one in 2007. We have also seen Google test green backgrounds and then even test going back to a flavor of blue and yellow backgrounds together.
Forum discussion at Google Web Search Help.