The color of your Adsense ad blocks can really make or break your sites profitability. Many people just use the standard Google color combination and never experiment. This to me really limits the earning potential you have with Adsense.
Because of my own curiosity I recently to took the ads on one of my sites and changed the colors from a color that blended with the page color (they were a light brown) scheme to standard blue color html code #0000FF. I did this because I have read so much that the Standard blue color is the universal color for links and people tend to associate this color with a link and will be more likely to click it.
The site in question has a mid double digit CTR and has had about the same CTR for over a year. The site gets about 50 visitors a day from various sources.
The day after i changed the colors from brown to blue the CTR fell in half!! It has been this way for seven days, i am changing it back tonight to get my earnings back inline.
This was a real eye opener to me as everything I have read over the past two years has stressed blue as the color of choice. I have recently heard rumblings of Red being a high converting color, this will be my next test to see if Red beats a blended Ad unit!
Keep in mind that I only change the color of top the Link line in the Adsense and I leave the text and everything else black. I also run no border and use a background the same color as my site.