There are certain apocryphal comments which become widely accepted in the absence of evidence because they seem to express an essential truth even if they were never uttered. We do not much care whether Voltaire ever said "I disapprove of what you say, but I will defend to your death the right to say it." The sentence, which does not appear in his works, clearly sums up a vital liberal attitude that we connect to Voltaire.
The same is true of Henry Ford on consumer choice. His comment, whether he ever said it or not, that you could have any color so long as it was black, meant first and foremost that he was confident in his product. Ford did not feel the need to indulge in eloquent salesmanship. His message was simple: "Here is the product, cheaper and better than you can get it elsewhere. If you don't want it on my terms, there are plenty of people who do." Of course, this is in itself a style of salesmanship, still used very effectively by brands like Apple today.
Another point was Ford's commitment to standardization, which lowered costs by a greater amount than he thought he could raise prices by offering the Model T Ford in a variety of colors. Black is a stylish and practical choice of color for a car. Many people would presumably have chosen black anyway and others were probably relieved not to have to choose. Ford chose standardization over variety, and the choice paid off.