Gouache (pronounced gwash) is my favorite medium for so many reasons!
It is rich, opaque and thick so I can get really bold, vivid color if I want or add more water to make it less saturated. Look at the variation below. Some elements are more translucent and some are very opaque.
It's water-soluble so no mess on clothes or anywhere else! I'm a messy painter and impulsive to so I sometimes have ruined clothes with acrylic.
I can create layering, especially light over dark as in the painting below. See the white buds over the dark vase? I can't do that with watercolor. I can with acrylic or oil but they aren't water-soluble.
It dries to a delicious matte, almost chalky finish, nothing shiny or plasticky looking like acrylic. Since it doesn't absorb into the paper, rather it lays on top, not like watercolor which stains the paper. This allows me to overpaint with any color. See below how I painted the lighter teal leaves over a darker leaf in the background?
Gouache particles are typically larger than in watercolor too, so there is real "tooth" to the paint. In fact, I can actually hear the paint going on the paper if I haven't added a lot of water (love that sound). And when you touch it you can feel the paint. These larger particles also make it heavier and more reflective.
Unlike watercolor, gouache doesn't rely on the whiteness of the support you're painting on to show brilliance. It has a white color which I used in the background on this piece to create more texture.
It can be mixed with watercolor paint. This is a nice feature in case I want to mix a color differently or want a more translucent wash quality.
It's very portable and travel-friendly, I've taken my little containers to St. Barts, Italy and around the U.S.
So, if you have the urge to try playing with gouache then I suggest looking at the resources on my website for some reasonably priced options. And of course, I show you how to do this in my online class on Skillshare which is essentially free because of my teacher referral link.