To help keep my color in place while eradicating flakies, I coat the length of my hair thickly with conditioner before I use my dandruff shampoo. I leave the conditioner in my hair while lathering just my scalp with the medicated shampoo (after all, it's only your scalp that's the issue here). After cleansing my scalp, I simply rinse my hair in cool water without actually lathering the rest of my hair.
This is actually similar to a growing hair phenomenon called co-washing (short for conditioner washing which, as the name implies, uses only conditioner to wash the hair). Anyone tried it? What did you think? Did you buy one of the "cleansing conditioners" made for the purpose, or did you just use your favorite standby?