AdSense and their usual "Optimisation Tips". Among them is this gem.
Match border and background
Match the border and background colour of your ad units to improve performance.
Matching the borders of your ad units to their background colour is a subtle style change that can lead to improved performance of your ads.
Choosing the right ad styles can mean the difference between ads users notice and click through, and ads they skip over...
Now I might be a bit thick, but doesn't "Match border and background colour" - in my case white - effectively eliminate the border entirely?
Also why do some of these suggestions seem to be at odds with best practices for user experience as well as not drawing undue attention to the ads?
I dunno, it seems the left hand of AdSense remains in conflict with the right hand of AdSense. I always take the cautious, conservative approach.
As for "ads users notice and click through, and ads they skip over"? As far as I know I don't simply get paid for click throughs, I get paid for clicks where the advertiser sees some satisfactory result from the visit.