How do you dye a hair system without staining the base?

No method is perfect but an easy way is to dip a comb into the hair dye and comb the color through the hair without saturating the base. Getting even a little amount of dye on the base for a short period of time will stain it. Also, don't keep the color on for the time mentioned in the instructions, 5-10 minutes should be enough. Color check every few minutes to make sure your not ruining that expensive thing.