As someone who is hopefully a rising member of the Classical academy, let me state plainly that I haven't the slightest aesthetic affection for any of the popular 'sets' of Greek and Latin texts. The Green and Yellows look like they were modeled on two nicely mowed fields of bleached grass. The Bristol Classical press consistently chooses the cheapest possible graphic images for their editions, and the OCTs are motley array, the kind of family that you'd swear was just adopted. The Loeb library has a nice look, and I appreciate the small size, but their consistent coloring gives rise to the problem that lexjulia has just brought up! I'm guilty of the same mistake. Finally, I'll add that the new volumes that Oxford released are all the same sharp blue with gorgeous (yet illegibly fine) gold lettering.
Also, I'll add that digital books are about to make all of these quibbles quite irrelevant. We're sitting less than 10 years from the day when readers can customize their Green and Yellow's to feature any shade of putrid grass that their minds could possible imagine. Just imagine a digital Loeb text in Times New Roman or Helvetica—reader's choice. We're on the brink!