In case you missed it, Google's AdSense Optimization page has a section about rotating colors in your AdSense Ads easily.
...rotating color palettes is a simple way to add variety and freshness to your ads. All you need to do is hold down the Control key and select up to four color palettes when generating your ad code in the Ad layout code page of your account.
This technique can be great for sites with return visitors, so they notice the ads and reduce user "ad blindness." As with any changes, do as test to see if you need all 4 color rotation options,and what color combinations work best.