I’ve built a lot of model cars in my time and I try to use primer as close to the colour that I’m going to be painting the car. With dark colours its not a big deal but when you get into the various shades of red you might want to think about a red primer.
I had the same problem trying to match some CP Rail red on some old Athearn GP’s.
Wasted a bunch of money on hobby. paints. You may want to try an autoparts store. They usually have a good selection of Duplicolor or similar paint in spray cans.(just a thought) I found some $1 a can red primer that was a really good match for my GP.
I’ve also gone to Home Depot with a car or loco and had them put it in their paint matching thingy and mix me a quart of enamel, but I used that in my airbrush.
I’ve got gray primer. That would cover nicely.