On 10-19-2015 I was on a flight from louisville to Phoenix arizona. I was seated in a window seat on the right side of the aircraft. We were at cruise altitude of 36000 ft over I think was colorado, the morning sun was on the left side of our aircraft. I looked out the window and saw a contrail that had a dirty smoke look about it. I thought it may be another aircraft near us. I began looking for the other plane but never seen it. After another 5 minutes we began to get some cloud cover under us and I noticed the trail again, but now I could see a very white round shape at the front of the contrail. I got out my phone and began recording. It is difficult to see however it was there and it did not look like any aircraft that I have seen.