When you dye your brows (using a brow dye designed with a special formulation specific for brow hair), the pigment coats the brow hairs making them look thicker.
When you request this service your brow artist might only need to darken the inner corner and outer tail of your brows to add definition, or she may decide the entire brow needs tinting. The dye only takes a few minutes to activate, depending on the color and boldness you are trying to achieve.
But brow tinting is not only for brunettes, it can be done by any woman or men with any hair color to help you achieve a very subtle look or give you a more striking look.