On early color computers, it was possible to add a feature by which you could turn off the color burst output, restricting the display to black and white but making it significantly sharper and clearer; this was useful for text. I don't know how much it cost to provide this feature, but I am inclined to think it would be useful for any machine intended for serious use rather than just games; its historical rarity suggests either the cost was nontrivial or there is another issue I'm not taking into account.
The Apple II had it from early on (including a useful mode where you could have most of a screen of color graphics, with four lines of crisp black and white text at the bottom).
The Tandy CoCo tried to provide it, but the first version allowed the color burst to leak through, and a revised chipset that would have fixed this, was rejected in testing because it broke games that had been written to exploit the artifact colors in what was supposed to be black and white mode.
Did any other early color computers (that output RF or composite video) allow the color burst to be turned off?