If you have strong value contrast in the 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 have black and you put any color next to it that color will look probably look great because it's next to something that has no color, but also because it is 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 strongest ways to make color rich is by putting 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.