If you have strong value contrast in a painting, you will notice that first. Secondly, color will be seen. Value contrast doesn't necessarily reduce the richness of color. For example, if you put any color next to black, that color will look great because it's next to something that has no color, but also because it's next to something with a much darker value than itself. This is an example of color being made to look richer with high contrast.
If you can imagine taking away value contrast in a painting, there would be little to notice except the slight differences in color, but the painting would not be very engaging from a distance, because we would not see value contrast.
One of the easiest ways to make rich color, is to put colors next to other colors that are different in value, temperature, and saturation. A moon in a night sky is remarkable, because the dark night sky is different in value, temperature, and saturation, compared to the light yellow moon.