Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.
Larry, I have been doing paint and body for close to 35 years. The most important thing dealing with this issue is consistency. If the sealer/primer has a noticeable effect on the final look, your paint is sprayed on too thin. The main thing a single color base guards against different shades in the final paint, if the color coat is too thin. The color coat shouldn’t be sprayed on too thin, or it will look bad. The color coat has to dominate, and completely cover the sealer/primer, no exceptions. As far as different looks, things like humidity, and even air pressure differences can cause final color mismatches.
So what can you do to make it look perfect and match. Understand that the color coat has to dominate period, no exceptions. Your base coat.....it is a good thing to start off and have the base all the same color. If you get the color coat too thin in places, and this does happen, it will hide the problem. If it looked like a dalmatian before you sprayed the color on, and you have thin in spots in the color coat, it will not look good. So a single color base coat serves mostly as insurance.
When it comes to paint I am a perfectionist, and I am fanatical about the process, all of my buddies tell me. You will see a lot of advice from amateurs, or people without much experience, there is more bad advice than good out there. Don’t worry so much about the sealer/primer color. I do get real picky when I am painting, but I save that for the things that matter the most, like surface prep, quality materials, good equipment, and a clean well lit place to spray, concentrate on these things and you should do well. Using a single color base is good, gray or white should produce the same end result with the proper amount of paint applied over them, remember the color coat has to dominate, if you can see through it, like if it changes the final color, you did something wrong. Go over all of this and if you have any more questions at all, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.
I do not get paid for my work unless you rate at 3 to 5 Smiley Faces or Stars, a bonus is always greatly appreciated. If the answer is not clear, let me know what additional help you need, and I will be happy to assist you further.