Google AdSense users who use the "alternate ads or colors" feature and try using the "fill space with solid color" option have been experiencing issues recently. In this case, when a publisher tries to adjust the color of that space to a new color, it simply won't save.
A Google Groups thread has been tracking this issue since Monday and it still appears to be an issue, even though AdSensePro Ashley, an official Google representative, has confirmed the issue and said it was fixed already.
On the afternoon of March 11th, Ashley said, "our tech team have informed me that this issue has been resolved." However, additional reports have come in to say otherwise. AdSensePro Ashley has confirmed the new reports and has once again submitted the issue to the tech team.
Forum discussion at Google Groups.