With all due respect to other's opinions, a well dressed man would never have as his only suit a black suit. It would always be appropriate for funerals or evenings out at the opera, but never, ever for weddings, confirmations, bar mitzvahs, company parties etc. Blue is the right choice. Or a dark grey. Not black.
There are exceptions to this, of course, as there always are and always should be in matters of taste and style. The exception would be if you're in a creative field like design or media or advertising. That's a different set of rules (and make no mistake, there are even stricter rules there than elsewhere) most of which I can't help you with.
One last thing. Regardless of what you go with, a well tailored, i.e. good fitting, suit always looks better than something that may be more expensive but fits poorly. Don't skimp on the tailoring.
The Definition of a Gentleman: Someone who is never rude, except on purpose.