This question already has an answer here:
All my life, when the question arises why we wear a black hat over our yarmulkes, the answer is that we do so to have a "double covering" when we pray. This implies that one covering, such as the yarmulke, is not enough, but one should have two layers on his head when he prays.
From where does this idea stem from? I have not been able to track down a source within halacha or Chassidus. I assume this idea is a minhag Chassidus, but why would having two head coverings be any better than one? Is it the idea that "more is better"?
Some people (even myself!) are very makpid to have two head coverings when they pray: a yarmulke and a black hat. Why?