Gouache/body color/opaque watercolor/guache, is a kind of watermedia. It is paint consisting of pigment, water and a binding agent.

Gouache has a considerable history going back over 600 years. It is similar to watercolor because it can be rewet and there is special paper for this kind of paint.

Furthermore you can correct mistakes easily if you know how to do it, the artist Grace erotti made a video about this on her youtube if you need help.

(Source: partly wikipedia)