If you are painting with watercolour, we recommend Designers Gouache as the best choice for opaque techniques. Known as the opaque watercolour, Designers Gouache has a matt, flat and highly pigmented colour, and is made with gum arabic, giving it superior flow qualities. It’s fully intermixable with watercolour.
While it’s possible to create this effect with acrylic, the technique needed is time consuming, as you would have to thin the acrylic considerably. Acrylic also dries to a waterproof finish, giving you less flexibility for subsequent layers, and the acrylic binder may damage sable brushes.