User blog comment:TheFruitless/Kyle's and Butter's eye color./@comment-71.207.115.154-20120111031655

Look at it this way: Stan is based on Trey Parker, and Parker's eyes are blue -- coincidence that Stan's eyes are blue too? Perhaps, but I think not. Since Matt Stone has green eyes and Eric Stough has blue eyes, those are the colors I'd guess for Kyle and Butters.