The blue hour is that time before sunrise and after sunset when the sun is below the horizon yet there is still light to see by, when the the light is actually blue.
This shot was taken well into the blue hour and adjustment were made in the color of the image to balance out the blue.
Here is a few images from a recent real estate photo shoot.
The unit won first place - best of show at the 2012 Parade of homes. Mary Kay Anderson of Dunham Company is the listing agent and did the staging of the home, it really is beautiful.