I've never had scalp issues, but I second the Nioxin for color retention.
It's great for color treated hair. Very mild and smells great. Their scalp
therapy conditioner is also really great if your hair responds poorly to
static or gets frizzy a lot. It's expensive, though. I'd get the big 34 oz.
bottle or at least a 20 ouncer. The small bottles will set you back a bit in
cost and since their shampoo isn't very thick, you'll use it up quite fast,
most likely. Smells so refreshing and nice, too. I love Nioxin. I even have
a Nioxin hairbrush!
JN