Black Opal is a wonderful color that is unique.
Had a '97 black opal C280 that I bought in '96, which I recently traded-in. Over the course of 6 years, 90,000 miles and lack of garage during 6 months of ownership,absolutely no swirls, ever. Then again, it may be related to the softness of the current water-based paints, although I vaguely remember that the same paints were used back then. Even so, a good polish followed by wax will go a long way. Dark colors with metallic flakes (black opal, obsidian black, jade green etc.) will hide the swirls better that flat colors.