Gouache is an opaque watercolor and is not used to build up transparent layers. Gouache paint has Chinese white or a type of chalk added to the pigment. It is thicker than watercolor paint and is not absorbed into the watercolor paper. Gouache can be used in a watercolor painting to apply light colors over darker colors, creating flat color areas. It can also be used to reintroduce white highlights into a painting, when the white of the paper has been painted over. Gouache is generally sold in tubes.

Gouache is often used by illustrators and is well suited to airbrushing. The paint is applied in thin layers, and the resulting painting has a matte finish. In order to retain this matte finish, care must be taken not to mar the finish with fingerprints or scratches.