The neck redness is called Poikiloderma of Civatte, which means blotchy skin named by an old French skin guy named Civatte. It comes from chronic sun exposure and doesn't go away. There's usually a zone of clear skin right under the chin in the center, where the chin has protected the skin from sun exposure. Most people don't treat this, but if you want to look into it, consult a dermatologist who uses lasers or similar devices, which may be able to soften the redness. Also, you'll get the kind of definitive diagnosis I can't give you from a distance, but that's what it sounds like.
Best.
Dr. Rockoff