You need to use a strong shampoo like one for oily hair or something.(If Prell is still available get that) That will help..definitely NOT one that is gentle or for color treated hair.
And after all that shampooing, i'd go with a good oil treatment. You can also buy coconut oil and slap some of it on and slip a plastic cap over it for a good 30 min then shampoo out. It is a great treatment!
I am a liscensed stylist.