Read the article again. Companies can in fact trademark a specific color and they do - T-Mobile magenta is specifically mentioned.
If T-Mobile magenta shows up in a photograph or a painting, that is, of course, not a problem, but if it shows up in another corporate logo (the article specifically mentions Engadget Mobile), T-Mobile gets to sue and wins.
Engadget Mobile's logo is still the same color, so I don't think T-Mobile sued and won. They simply mailed a nastygram, which anyone can do for any (or no) reason.
If T-Mobile magenta shows up in a photograph or a painting, that is, of course, not a problem, but if it shows up in another corporate logo (the article specifically mentions Engadget Mobile), T-Mobile gets to sue and wins.