Apparently, in Episcopal churches, it’s kind of a tradition to have their doors painted red. Here’s why:

In the earlier days of the church it was understood that a soldier could not pursue an enemy that had entered through the red doors of a church. The red doors were a symbol of refuge and sanctuary for all people who entered. To all concerned the red on the doors signified the blood of Christ that had been shed so that all who came to him could be saved. Anyone who passed through those doors was safe as long as they stayed behind them.

As I recall, that concept is played upon in the sci-fi “classic” Highlander, when the two remaining immortals, Connor MacLeod and the Kurgan agree to meet in a church, according the ancient rules of sanctuary. Although, I think that in one of the later Highlander movies, that rule is broken, and a fight does take place in a holy place. Anyway, I’ve also heard elsewhere that red doors go back to the original Passover tradition in Judaism.

The name Passover comes from when the Angel of Death passed over the homes of the Jews, because they had been forewarned, and had put lambs blood on their doors, so that death would spare their first born child.

Also, there’s this stream in Christianity that says the shedding of Jesus’ blood was basically equivalent to this Passover blood sacrifice:

Sin causes men to go to hell. The only way men can attempt to ‘neutralize’ the damning power of sin is to make a blood sacrifice. Yet, blood sacrifices do not change men’s hearts, which remain damningly sinful. This is known as a ‘Catch 22′, or a no win situation. Christ changed all of this because he could change men’s hearts. If we ask Christ to be the Lord of our lives, he will not only change our hearts, but erase our sins from the Book of Life. His is the blood sacrifice for all men. He died upon the cross in total innocence as a worthy passover blood sacrifice. Christians will be passed over for damnation just as the first born Jewish sons were passed over for death.

On a tangentially related note, red doors are also featured in feng sui:

A red door can be used with the intention of protecting the home and those inside, especially if your house is at the end of a T street intersection. Red can also be used to attract chi towards the door

Here’s another quick thing about doors in feng shui.