In Medieval times, a red door on a church signified sanctuary- a place where an accused criminal could be safe from arrest. The accused could ask for protection while in the church.  If I remember right, the protection was for up to 14 days.  Don’t quote me because I’m reaching way back to dig this info from the old memory bank (and it could be 40).  The right to sanctuary was abolished by James I in the early 1620s.  There is still a tradition of red doors on many churches. 

Red doors have always fascinated me. I find them very appealing.  I have quite a collection of pictures of red doors.  Seems like I collect them.  This one is in the Chelsea area of NYC. I love the detail at the top.