Aaron Wall noticed that Google is testing a new AdWords background color that is ever so slightly different from the current one. The current color is #FFF8E7 and the test color is #FAFAE9.
The test color seems a bit darker or muddier to me but I am not sure if that is enough to increase clicks on the ads. Do you think one color is more blended into the organic results than the other? I guess Google is trying to test it.
Here is an animated GIF between the two:
July 2010 - Pale Purple:
April 2007 - Yellow:
Prior - Blue :
Test of Green May 2008:
They even tested muticolored backgrounds.
Forum discussion at Google+.