There is no record of Henry Ford having ever said this, in a serious tone. In his autobiography, he mentions it as a statement to his salespeople, but the reality is that the Model T was available in a wide range of colors, including fire-engine red, and hunter green.
From his autobiography, Chapter Four:
This season demonstrated conclusively to me that it was time to put the new policy in force. The salesmen, before I had announced the policy, were spurred by the great sales to think that even greater sales might be had if only we had more models. It is strange how, just as soon as an article becomes successful, somebody starts to think that it would be more successful if only it were different. There is a tendency to keep monkeying with styles and to spoil a good thing by changing it. The salesmen were insistent on increasing the line. They listened to the 5 per cent., the special customers who could say what they wanted, and forgot all about the 95 per cent. who just bought without making any fuss. No business can improve unless it pays the closest possible attention to complaints and suggestions. If there is any defect in service then that must be instantly and rigorously investigated, but when the suggestion is only as to style, one has to make sure whether it is not merely a personal whim that is being voiced. Salesmen always want to cater to whims instead of acquiring sufficient knowledge of their product to be able to explain to the customer with the whim that what they have will satisfy his every requirement—that is, of course, provided what they have does satisfy these requirements.
Therefore in 1909 I announced one morning, without any previous warning, that in the future we were going to build only one model, that the model was going to be “Model T, ” and that the chassis would be exactly the same for all cars, and I remarked:
“Any customer can have a car painted any colour that he wants so long as it is black.”