Google sent out an email to all publishers that they will change the default color palette from Seaside (formerly known as Mother Earth) to Open Air. They say the change is because "many publishers prefer the cleaner look of this palette and have also seen that a blended color palette performs better for them."
Here is the difference:
You notice that this really blends the ads into whatever the site may look like. It is like hiding the ads, and displaying them as the text on the page. That is why many publishers opt for the borderless style. But as a default... I am not sure...
Forum discussion at DigitalPoint Forums & WebmasterWorld.
