Activity

It’s possible. It normally depends on shade of the color itself, plus the coating. If it’s a particularly bright color, a single coat can appear darker then intended. Just give it another coat, and if that doesn’t solve your problem, then it’s an issue the paint. Either you managed to get a bad batch, or the paint you’re using is too translucent.

I had that problem twice in the past. Not with Tamiya spray cans, but an other brand. The paint cans probably got frozen and the pigments starts shifting. At first I thought I didn’t shake them well enough. The last quarter of the can the color was fine. The first three quarter the color that came out was a lighter and duller version of the paint. It was a gloss paint, but came out matte.
If the white paint you used came out good, you can safely presume the grey primer doesn’t effect the color. This is a advantage of spray cans. The quantity of color that comes out is so vast, mostly it won’t be affected with the color underneath. Using a airbrush is a different story.
You could try spraying a clear gloss on top of it, but I doubt it will give you the result you’re looking for. If you bought the spray can in a hobby shop, just return it, explain your complaints and they should give you a new one. At least, they did give me a new one twice. Good luck