A dark grey can likely be worn at more times and in more situations than can black.
I have an intense dislike for the color black. And it's so unflattering on so many people. Really, its only benefit is that it is universally considered dressy by everyone, including the uninformed, though that can actually be a negative, since it's the kind of thing most people would only wear to a funeral.
For general wear, gray or navy blue would be more useful.
Preferences can vary by region, though. Where are you located?
Charcoal Gray. Black suiting is nigh unto universally a food service uniform color.
If you can swing it, get a Navy Blue suit in a slightly different cut as well.
Just to add to the pile, dark grey or navy blue are the best options for a first suit.
Black is reserved for tuxedo's, funeral attire and the MiB. I know American culture differs a bit on the subject, but in Europe technically there is no such thing as a 'black' suit. It might be very dark grey or blue, but not black.
Charcoal grey is very good for your first suit, as it is acceptable in every situation. Dark blue might be better, depending on your appearance and line of work. If I may be so bold and simply assume you look like a cartoon-character Irish man, blue would be better as it isn't as 'hard' on fair skin.
Charcoal first (do it all suit, weddings, funerals, interviews)
Navy second (can be jazzed up a bit more with coloured shoes shirts, ties, pocket squares for more "social/celibratory" type gatherings)