If your goal is to have people click on your ads, what other denominator is there than the click-through percentage? Google is a middleman for advertising, it's not for them to judge whether their viewers are worthy of clicking on their ads.
And do you really think there's a socio-economic divide along the lines of blue vs. yellow text ads? Because that's pretty ridiculous.
Lowest common denominator? Publishers want users to click. Google wants users to click. Advertisers want (good) users to click.
Who loses here, besides the person who thinks yellow is "bad design?" Your customers have the final say, not the designer.
Should you cater to the lowest common denominator and be the Microsoft of the web, or try to do the Best Thing and have a smaller market share but of much higher taste and disposable income, aka the Apple ?