"We're asking that publishers use good judgment on how much they change the colors or formatting of the ads to ensure users don't confuse third-party ads with Google ads. Proximity plays a role as well - if you're placing the ad units directly adjacent to one another, we'd ask that you use clear borders and offsetting colors to indicate where one network's ad unit ends and the other begins. If the ad units are on opposite sides of the page, using different backgrounds colors and/or a different color scheme for ad text and borders should be fine. Ad units that are virtually indistinguishable from the Google ads on a site would certainly violate the spirit of this policy,"