Black may look good at first and probably does hide coralline but I wouldn't buy one with black silicone myself. My tanks (5,7, and 8 years old ) all have some tearing and jagged edges on the silicone. It's a natural consequence of cleaning and scraping the glass. It's not that noticeable with clear silicone but I suspect it would be with black silicone.
I have black silicone on a tank just over a year old and I can see tearing already...