Seeing Lemon's apartment entry door made it clear that: 1) painting it black gives it a little more visual heft, 2) it evens out scuffs, gouges, and fingerprints that often mar the front doors of apartments, and 3) a black door looks great with standard brass front door hardware - it even makes those clunky d-shaped locks look better!
It also surprised us that we liked the black door set in a white-painted casing. This allows you to carry white trim throughout your apartment and go black only at the front door. We wouldn't like this nearly as much if the casing was also painted black. (Images: 30 Rock episode 316: Apollo, Apollo)