To darken bleached hair, first apply a red or gold permanent dye, then apply the desired shade of demi-permanent dye. The first color fills the hair's cuticle so that the second color can be applied.
If the darker color is applied without the bright base, the hair's color will turn a muddy, dull shade. This is because the bleaching process works by damaging the cuticle. The damaged hair cuticles have to be filled in with a brighter color to repair the damage in order for the new color to stick and give hair a shimmering appearance. If a red tone is desired for the final color, apply a red permanent dye. If a brown or dark blonde end result is desired, apply a gold permanent dye as the base color.