Blond highlights can be an eye-catching addition to hair. However, if they are too light, they may not blend properly with the surrounding hair, still bringing attention to your hair but not in a desirable way. In general, blond highlights should be no more than three shades lighter than your natural base colour. If your highlights, whether through time in the sun, a recent salon visit or an at-home colouring, are too light, they can be darkened in a few minutes with the right product.
Apply a demi-toner purchased at a beauty supply store in a level 7 neutral shade to the affected sections of dry hair, beginning at the root and ending at the tip.
Cover the hair with a plastic cap and allow the product to permeate hair for 10 minutes.
Shampoo hair, rinse well, then dry and check colour.
Repeat the toner process with a level 6 neutral toner if the highlights are still too blond.
To ensure that the blond strands stay dark, shampoo your hair once a week with a shampoo made for brunettes. This will deposit small amounts of colour into the highlights as the demi-toner begins to fade.
Use only toner in a "neutral" shade. Do not use toner that specifies "ash" or "warm" without consulting a hair colour professional, as these tones can react with current hair colours and cause the hair to turn shades of green or orange. Do not worry if the toner gets on the darker, unhighlighted areas of the hair, as it will not affect these portions.