When I am painting light and shadow I find it useful to ask "what is the dominant color?" It is almost always a cooler, darker, and more neutral version of the surface it falls upon.
Here's a detail of an image full of shadows. Notice that the shadowed part of the yellow blocks are still mostly yellow, even though the color is darker and more neutral than the color in sunlight. Yellow is the dominant color.
Take a look at the red cap on the white tank. How are the shadow colors different from where they are in sunlight? Like the yellow shadows, the red shadow is darker than the sunlit area of the cap. What is the dominant color of the red cap in shadow? Still red, right?
Now what about the shadow on the white tank? It's pretty easy to see that it is darker. Is it cooler, as well? Is it more neutral?
The photos below offer opportunities to practice observing and mixing shadow colors. If you'd like to create a context for the shadows feel free to make a proper painting from one of the scenes. If you just want to experiment with the colors you can try adjusting how light and dark they can be, or make the dominant color more or less intense, or more saturated. See if you can find the point beyond which the shadows still look natural.