I go the black one and when purchased from the dealer, I opted in for Autoglym lifetime lifeshine (got a decent deal). Don't have much experience with it as having it only for a week now but it was immaculate for day to day driving around town when it didn't rain but yesterday I took it for an hour trip via the motorway and the weather conditions were treacherous. It got dirty really bad (at least it looked like it!) but then when I left it overnight and it was raining again, this morning you can only see some remainings on the tyres and side mirrors - everything else washed away and it's back to, maybe, day 3 body-wise. I reckon without the Autoglym, I'd have to get it washed today.
Yes - it's getting dirty like any other car. Yes - you can see it probably more than on the brown or grey car (defo less intense than on a white car

) but that's only if it's really dirty (i.e. after some cross rallying

) and that black paint is a head turner
Feel free to pm if you want any pics etc.