Paints of all colors reflect different amounts of light. It’s easy to see that dark colors like deep blue reflect less light while bright colors like lemon yellow reflect more light.
The same holds for gray primers; dark gray primers reflect less light while light gray and white primers reflect more light. If the amount of light reflected by a topcoat color is matched by a gray primer, the eye perceives improved coverage of the topcoat.
For example, deep blues look better over dark gray primers while bright yellows look best over light gray or white primers. The Primer Decider makes it easy to pick the right shade of gray primer for your specific topcoat color.