My dad has had skill dying wool hose from off-white to various shades of blue, green, and pink. But trying to get something from navy to black might not work quite as intended. Why not keep it navy blue? Too many people wear black kilt jackets anyway. Mine are royal blue and burgundy and I never am wearing what everyone else is.
But if you are intent upon the black, perhaps just waiting until you get what you want will be better. Or maybe you should get the navy blue and use it until you find a good deal on a black one... that is unless somebody here has done what you're trying to do... but I doubt it. Kilt jackets aren't any trinkets to experiment on too often.