Apparently this is considered the normal, default pronunciation in General American. Look at, and more importantly, listen to red at the Sound Comparisons site. Notice that the General American pronunciation is given as
On the other hand, apart from the up-talking teen-aged boy’s pronunciation provided in the “General American” version, all the other North American versions use the
[ɹ] version instead of the
I must confess that I myself am hard-pressed to hear any difference between those. Probably that’s because it’s not a phonemic distinction, but possibly because it doesn’t actually exist.
Another place that is alleged to have the retroflex version is Lewis, which I presume they mean the Isle of Lewis in Scotland. They give
[ɻɛ ̝ˑd ̥] as the pronunciation. I can’t hear that being a great deal different either, so the retroflex aspect isn’t obvious to me.
If you really want a different r, listen to the one from Buckie, Coldstream, or South Wales, where it is a true rolled
[r]. You might also check out their respective pronunciations of rain, right, and ring, which all display the same sort of regional variation as red does. Oddly, the Lewis pronunciation of ring sounds like a rolled retroflex to my ear.