No, Sea Blue has touches of gray and green to it. I’d suggest starting with Royal Blue and darkening that. If you look at late war photos of Corsairs, unlike Grumman, Vought stayed with Insignia Blue, and it contrasts with the overall Gloss Sea Blue finish.
I don’t have royal blue but I do have flat blue. Wonder if I can start from there and darken? Also any idea what is a good color for darkening blue without shifting its hue? I am getting better at color theory but I still struggle with blue
I’d suggest trying black to darken the blue. Obviously you’ll need to experiment to find a ratio that works, say three or four parts blue to one part black. But you’re going to want to start with a blue that is not having any grayish or greenish hue to it.