These shadows are not all the same color, or are they? If you're making a watercolor painting of this array of shapes couldn't you use the same gray to darken the shadows of the grass and the pavement, and let the local color show through? Or would you have to make separate colors, one dark green and one dark blue-grey?
Try it both ways and see which technique you prefer.
Below is a painting by John Singer Sargent. Can you tell which method he used?
Here you can see that not only does the color change as the shadow passes over different local colors, the value of the shadow also depends on how dark the local color is. The shadow on the red shingles is darker than the shadow on the white window trim.
Here are some images with sunlight and shadows. You can make a painting from one, or you can just paint patches of local color and the appropriate shadow color.