The best characteristic of semi-permanent hair color, which also applies to any brand, is that it is safe for hair that is fragile or has been damaged. Because semi-permanent hair dye molecules mostly cling to the outside of the hair shaft without penetrating it, this type of hair color is much gentler on the skin than permanent or demi-permanent hair dye.
Semi-permanent hair coloring is not mixed with a developer such as ammonia or hydrogen peroxide and therefore don't cause damage to the hair. It is particularly beneficial to thin hair since the coating of color on the outside of the hair shaft helps provide a little extra volume to the hair's overall appearance. In addition, they even provide some protection to the hair's cuticle against sun or heat damage. Semi-permanent colors also tend to look particularly vibrant when first applied because of the way they reflect light.
Semi-permanent hair coloring does not cover gray hair well, but it can be used very successfully in weaves and highlighting to blend gray hair with the added colors. Some semi-permanent colors, such as Clairol's Advanced Gray Solution, are designed specifically for the blending of gray hair. Semi-permanent hair lasts from four to eight shampoos and must be reapplied every few weeks to maintain a consistent look.