Hair is darkened after bleaching by applying a hair dye. Bleach strips the hair shaft of its natural color pigment, and the only way to re-pigment the hair is with a dye. New hair growth retains the original hair color.
Three types of hair dye are available for darkening hair. Temporary hair dyes coat the hair shaft with color. These dyes wash out after a few shampoos. Semi-permanent hair dye contains small pigments that bond with hair better than temporary dyes. Semi-permanent dyes last up to six weeks depending on the particular dye used and how often the hair is shampooed. Permanent hair dye contains a chemical to open up the hair shaft and allow the coloring to fill and bond with the hair strands. Permanent hair dyes sometimes fade with time or exposure to sunlight, but they do not wash out. Commercial dyes are available at department stores and beauty supply outlets.
Bleaching hair involves a harsh chemical process that dries and damages the hair shaft. Temporary and semi-permanent dyes are gentler than permanent dyes and make great choices for darkening bleached hair. When permanent dye is used, the hair needs to be conditioned regularly to decrease the hair's fragility. Many dyes come with special conditioners for aftercare.