Like many artists we often have more than one piece going at once. I'm no exception. I will sometimes have pieces in 3 or 4 different mediums going at the same time. This helps to break up the monotony of working on the same medium or piece for long periods and I find that it forces me to let my watercolours dry thoroughly before approaching them again because I always have something to work on. The downside to this is that you really need to keep record of the colours you're using from one piece to another. This is something I've learned to do anyway but it can be tricky.
Since finishing my Peek a Boo the other day, I'm now working on my acrylic monochromatic peony. From time to time I like to work in "Verdaccio". Verdaccio was created traditionally from a mixture of Mars Black and Yellow Ochre pigments & was used to establish tonal values in fresco painting quickly, creating a soft greenish-gray for the shadows of flesh tones. The old masters would often work in this style defining tonal values, forming a complete monochromatic underpainting used especially for portraits. It's a lot of extra work it seems but for me it helps to reinforce the importance of value in my pieces.
In the case of my peony, I am not using any ochre but rather Ivory Black and Titanium white to create the black to white values. Once I have the values where I want them I can then go over the piece with a thin transparent glaze with the colour of my choice and since the values are already there, I won't have to go and paint each area separately and hope that my values are correct.