There are some good reasons for unpredictable and unwanted hair color results. Several factors can influence the final color of the hair following the coloring process. During the first week after coloring, hair usually lightens, especially after a few shampoo cycles. This may help alleviate some color issues. There are a number of products to correct unintended or bad hair color; however, being aware of the following issues can prevent bad color before it happens.
For semi-permanent color, the final color is a blend of the natural color of the hair and the dye color. If the strength of the dye is too weak, then this problem can be even more pronounced. The advantage to this is that semi-permanent dyes do not last long on the hair and will wash out faster than permanent hair color, allowing the process to be correctly redone. This is an easy fix compared to redoing permanent hair dyes.
Bleaching and Color-treated Hair
In permanent hair coloring systems, bleaching the hair with hydrogen peroxide is required to remove the original color to pre-pigment the hair before application of a new color. Dyeing bleached hair brown can result in gray or ashy hair with a gray sheen if the dye does not take well. Also, previously color treated hair can react unpredictably with further color treatments if all of the previous color has not been totally removed. The use of some shampoos, which can deposit a layer of plastic on the hair, can block the action of the dye, making this issue more obvious. Since the final color is a mixture of different color dying chemical components, the color ratios must be altered and the dying process repeated with a corrected ratio if the final color is not what was expected. Since the dying process does damage the hair to some extent, changes in the final hair color outcome are to be expected. Only an experienced hair colorist can avoid situations like this.
Water Elements and Hair Chemistry
The presence of minerals, salts, chlorine or other contaminants in the water used in the coloring process can affect the final color of the hair. Since reactive dyes are used in the permanent hair coloring process, these minerals, salts and other ions can become part of the chemical reaction. Local tap water in homes and salons varies by location, making the results vary widely. Certain prescription drugs and a person’s overall health can also alter their hair chemistry that may affect the final hair color.
Coloring dark hair to achieve a desirable shade of blond requires bleaching followed by a secondary color treatment. Bleached hair can still have a yellow or copper shade following this process.
A violet-based color can cancel out yellow tones, and blue-based shades will cancel out copper orange hues. If the hair is lightened only a couple of shades with a permanent hair color, blue-toned shampoos have been formulated especially to combat this problem. This is the same principle that exists with skin color correctors where subtractive color is responsible for negating some visual color responses. If one adds a small amount of blue pigment to a cosmetic product, it will absorb some of the unwanted red wavelengths in the skin. Hues such as red, blue, green or violet are usually undesirable, unless these are the desired final colors. Light blond hair is notorious for having green highlights, and additional processing may be necessary to eliminate them.
Porosity and the extent of previous damage to the hair from the dying process can also affect the final hair color shade. Usually porous hair absorbs the color more, resulting in darker than expected shades. This is especially true of coarse and damaged hair, which is the issue in a majority of cases.