I suggest shampooing first to get a good clean start. Use something gentle and as natural as possible. I used to buy Neutrogena Shampoo when I wanted to get a good clean and strip away the residue. If you suspect a fungal thing is happening then I think a nightly treatment of coconut oil would be a good idea. Unless you want something fast - then go for the anti-fungal shampoo.
I know you love to color -- but most coloring agents are pretty harsh. You might just stay au-naturel for a year and see if things improve with the condition of your hair and scalp.