Google seems to be tested two new ad styles for their AdSense ad units.
One design places the enclosed arrow in a circle within the center of the ad unit and the other design uses a transparent white, with patterns through the background.
The first one was shared by Chris Jones on Twitter, here is a screen shot and notice how the arrow is in the center of the ad unit:
Also, a WebmasterWorld thread has an AdSense publisher complaining that Google is forcing an "ugly white ads with patterned background with white-grey stripes," on his ads, despite him not selecting those ad styles in the AdSense control panel.
Here is a picture he shared:
Google is frequently testing AdSense design tweaks, all with the goal of improving CTR and earnings.