Over the last few days one bone of contention between myself and my friend was about the colour of the socks that one shoud wear, as required by standard etiquette. I was of the opinion that the colour of the socks should match the trousers and he felte that it should match the colour of the shoes. I decided to check this out a few minutes ago and was happy to be unanimously supported by all the etiquette sites. So the rule is: The colour of the socks should match the colour of the trousers and the colour of the belt should match the colour of the shoes.
Here are a few links that will explain this and more about professional etiquettes: Etiquette Tips and Quick Fix Focus On Style- Matching Socks, Men's Style and University of Pittsburgh: Katz Graduate School of Business.