the customer (or client) is always correct. always.

if they don't like a color, change it. the site will look much better with an off-white background...you just haven't realized it yet. bet you didn't realize your client was a professional graphic designer.

if your client tells you "something about that font really bugs me. could you change it?" they really mean, "increase the kerning of the type and switch to a sans serif face." your client just didn't want to show off their mastery of typography...sorry, fontography. the type change will dramatically increase the readability and usability of the site.

if a client tells you to change something and then change it back to the way it was originally, don't get upset at having to do the extra work. after all, you've learned something important...the customer is always right...even when they initially appear not to be.