1: What happened to the people on the 4 missing airliners? Impossible to know exactly since the CIA had known hijack drills that morning, fake radar data was inserted and real rada data was replaced. The CIA planned to hijack airliners and fly them to military bases in "operation malgom virgo". They could have done it many different ways. It's easy to make airliners disappear if you are the government. A good example is MH370, even with working and up to date radar tracking technology, the plane and all passengers are still missing several years later.
If nature can make an airliner disappear, imagine what the CIA can do on a morning with known hijack drills. Obviously they killed all the passengers. If you don't think the CIA would kill americans, watch "CIA & Satanism" by Ted Gunderson.
2: Why didn't they paint the belly to be dark blue like UA175?: Impossible to know their reasoning, but they felt it was enough to just paint the tail. You can't deny the fact that they got away with it.
Even if you don't believe the video footage shows it was a military plane and that all the witnesses were wrong, the engine that flew out from the supposed U.A. 175 crash did not belong to any of the missing 9-11 planes, no U.A. 767 in history has ever used that engine. The engine is forensic proof, study the pictures and compare it to the model UA175 used. The case is closed.
Here is the web article comparing the engines ckpi.typepad.com/christopher_king/2009/09/murray-street-engine.html
Showing that the "hijackers" were nothing but CIA agents: www.youtube.com/watch
What happened to the 4 missing airliners? www.youtube.com/watch