Google refers vaguely to the "need for a new look" in shifting their top sponsored ad background color from blue to yellow today.
Were CTR's declining? We know that rotating ad design in banner campaigns sometimes props up CTR's. Personally, I haven't seen much evidence of declining CTR up there at the top, but you never know.
Another significant shift is not triggering a clickthrough unless the user actually clicks the link. It's been a bit cheesy that clicking anywhere in the box caused a click. So the result of this shift should be a noticeable improvement in ROI out of the top ad spots.
Fewer clicks, but more clicks that meant to click.
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