Hair-coloring agents, such as DYES, are chemical substances used to change the color of hair. DYES are the most common type of hair-coloring agent, and they work by temporarily or permanently altering the pigment of the hair. They can be used to cover gray hair, lighten or darken existing hair color, or create a completely new color. DYES come in a variety of forms, including semi-permanent, permanent, and temporary.