I've had this discussion with my paint rep for several years. My contention is that coverage is coverage. I use the 1" square self stick targets that are black and white checkerboard colored when I paint. It's known as black and white hiding. When you can't see the black and white through your basecoat, then and only then do you have "coverage"
For example, say it takes 4 coats of a yellow base to get black and white coverage. If you use a sealer that is close to yellow, you may think you have coverage in say 2 coats. But do you? No, the sealer is influencing the color you are seeing. Doesn't matter if your sealer is lighter or darker, you still don't have the true color of the basecoat until you have black and white hiding.
A sealer that is close to the basecoat will make you think you have coverage before you really do. Now I'm not saying it's not a good idea to seal with something close in color to the base. It makes a lot of sense, especially when it comes to those stone nicks and door dings that you'll eventually get.
Just my .02