Recently, with the rage of this "Feng Shui" thing going on these days, I've seen many more red doors pop up everywhere. I was doing some research today and came across this:
"Before the New Year, Chinese people clean their houses and wash their clothes. Many people put red paint on their windows and doors. Red is the colour of good luck in the Chinese tradition."
I do believe the religious context is the original reasoning behind red doors, but I also think it's recent resurgence is due to the Feng Shui craze.
I also came across this, which I found interesting:
"THE FRONT DOOR IS AN IMPORTANT ELEMENT FOR WEALTH, so try painting your door an auspicious color. If your door faces SE, consider painting it purple or a shade of purple. You can also paint it a rich green color. If it faces north, paint it black. If your door faces south, paint the door red to enhance your reputation and renown."
Either way, I think red doors look classy ;-)