This is a Good Way to practice your colour mixing skills. To mix your own greens you can use any natural pigment blue with any natural pigment green. I find even those that are not supposed to be paired up for warm/cold colour reasons are fine. I also use old residue on palettes of tertiary colours to darken greens. The key to mixing your own colours is to mix enough. And also, keep a written record of those that you are sure you will use again.
Watercolour will keep for years once you have mixed it so making too much is not an issue.
Underpaint all of the peas and pod with lemon yellow. Mix a range of light, medium and dark greens. When the underpainting is dry work light to dark, from the back of the composition. Use a large brush to paint the peas, leaving a light area to suggest a light source, bear in mind there is a cast shadow of the pea pod on the tops of most of the peas. This exercise illustrates that most peas are slightly different shapes, they are not perfect circular shapes that are uniform.
To make the cast shadow of the peas and pea pod: use a black or grey watercolour pencil and draw a line on the border of the pod and the peas. Take an appropriate sized brush and wet the line of pencil: works perfectly for a small shadow area.
The pea pod is not smooth so for painting that use a stipple brush or a natural sponge.
The background: I used a purple watercolour pencil, only a small amount and used a large brush to spread it and take the “whiteness” off the paper, which for such a green composition can appear rather stark.