Etching primer is the best primer for metal without a doubt. But all undercoat color, will have bearing on the top coat.
You just think you've covered it. Your eyes can still see the tiny bit of light that penatrated the top coat and reflected off the primer and back out again. Choosing primer color is important too, that's why it is offered in base colors (white, black, red/ brown, grey, etc).
So you likely ended up with a pale to dark green primer I assume. For dark colors, this usually works. But for light colors an extra coat will likely be needed. I prefer just enough flat, or a normal primer, to lighten a base before topcoat.
To really brighten vs a deep color saturation, use white or light grey first, then topcoat with color.
I.E. the etching primer isnt the issue, the primer color is.