I did an exercise in “negative painting” where you concentrate on the painting in the negative spaces. My teacher pulled a book sort of at random from the shelf and handed it to me, as I was a bit uninspired. This was by Linda Kemp, and it turned out to be a lot of fun. Not 30 seconds, but about 30 minutes.
Stage 1: create a pale underpainting, wet-into-wet, using Quin Burnt Orange (for Burnt Sienna), French Ultramarine Blue (for Cerulean Blue), and Phthalo Green (for Winsor Green).
Stage 2: after underpainting is dry, draw in the leaf and stems. Going wet-into-wet again, fill in the negative space with more value.
Later stages are yet to be done.