For our painting class we were required to paint three similar paintings indicating some sense of depth. The first one was meant to be a flat painting done in black and white (achromatic). The second painting was also done in black and white, but this time gradients (and a possible light source) were added. The final painting was the same as the second, but with a single colour added (monochromatic).
Painting with gouache takes a bit of getting used to. Especially blending colours is rather difficult to achieve, I think. It probably just takes practice :) Here's my paintings, yay!