I am in the process of installing two ceiling fans in my family room. They are both replacing existing light fixtures that are controlled from a single switch. Upon removing the existing fixtures, I've stumbled upon some confusing wiring. In one box I have two cables coming in... a gray cable containing a black, red, white and bare wire... and a white cable (with markings), containing a black, white and bare wire. The other box has these same two cables coming in along with an additional third white cable (no markings) also containing a black, white and bare wire. The ceiling fan has a black, white and blue wire along with a green ground wire. It comes with directions to wire to either the 3 or 4 wire comination, but assumes a single cable in the box. Any insights would be appreciated.