I had a 2009 in BGM - black granite metallic. I didn't do anything special to take care of it. I ran it through the drive-through car washes with the "touchy" scrubbers, not the touchless, which doesn't clean all of the dirt and film off.
I owned it 2 years and put 20K miles on it. The only special thing I did to it was what I learned from this website: I cleaned the paint using a clay bar, then scratch remover, then swirl remover, and finally wax. I did all of it by hand and it took me (a noob) a couple of days to do it. When I was at work a manager saw the car and about dropped his jaw on how smooth and perfect the paint looked! And I continued driving it through the "touchy" car washes after that.
Later that year I traded it in on a 2011 in RJT - red jewel tintcoat. What I learned with the '09 was that I needed a cheap random-orbit buffer to make my job easier, and it did! I owned that car 3 years and performed the same treatment 2 times. The second one was on Memorial Day weekend, resulting in what I'm using as my sig-pic at this time.
Other than performing that treatment, either yourself of having it done for you, I haven't found the dark colors to be especially hard to keep looking good.
Once when I owned the '09, my sister and I were driving by a dealer in a city way out of town and I saw a pearl tri-coat sitting on the lot. I really like that color, too.
What I'd really like is to have a car with a forest green interior, maybe with some tree-bark brown as a second main color and a camo theme on the trim. I've been in one car that had the dark green interior and I fell in love with it immediately when I got in to move it from the service drive to the parking lot. I worked at a Ford dealership at the time and have never seen another interior that color.
+1 on what
@nutcrunch says on other people's opinions. Find the color that really moves you and choose it. The only real complaint I had with my '09 BGM was that it was
all black, inside and out. On a lot of the Gen7 models the inside was available in a two-tone scheme but mine was black on black. It was okay but didn't have any color other than the thin gloomy gray trim pieces, which I was not fond of. (It was a dealer-trade and I never saw it until it was dark out, and only after signing the papers. My first-ever new car.)