Gouache paint is best described as:

Gouache paint is best described as opaque and water-soluble. This characteristic sets gouache apart from other mediums such as watercolor, which is typically more transparent and relies on layering to achieve depth and color intensity. Gouache achieves its brightness and opacity from the addition of white pigments, which provides a solid coverage over the surface it is applied to.

Gouache can be easily diluted with water, allowing for a range of application techniques similar to watercolor; however, its opaqueness allows artists to cover underlying layers more effectively. This quality makes it popular among illustrators and for design work where solid colors are desired. The versatility of gouache in mixing with water gives artists flexibility in adjusting the paint's consistency and working properties, further reinforcing its classification as water-soluble and opaque.