Stormy Sea vs Green RLM73

How close are they?

ΔE 9.9, close: similar, with a visible difference side by side. Green RLM73 is a little lighter, more muted than Stormy Sea.

Can I use Green RLM73 instead of Stormy Sea?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Green RLM73 is a little lighter, more muted than Stormy Sea.

Can I use Stormy Sea instead of Green RLM73?

The same difference applies the other way round: Stormy Sea is a little darker, more saturated.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.