Techno-Net informed me via Twitter that Google is testing yet another background color for the AdWords top ad spots.
This is not the first time they tried a purple or pink'ish color. In July 2010 they tested a pale purple color as a background image.
Currently, AdWords backgrounds are yellow, but here is what this off-pink color looks compared to the yellow.
For the previous color background choices either tested or tried by Google, see this post.
Forum discussion at Twitter.