"Keep a little bit of the root," Alvarez says. She recommends leaving one-half to one-fourth of an inch of hair at the roots free of dye. If you're doing a pastel color, she suggests leaving the ends or pieces in the front a little lighter than the rest of the hair.
Also note that you'll likely need to leave the dye on the wig longer than the instructions say to. "On average, I would leave color on for 30 to 45 minutes," she says. "Depending on the quality, you might need to extend it for 10-minute intervals until desired color is achieved."