Marine Mist vs Ion Blue

How close are they?

ΔE 7.7, close: similar, with a visible difference side by side. Ion Blue is more muted, cooler than Marine Mist.

Can I use Ion Blue instead of Marine Mist?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Ion Blue is more muted, cooler than Marine Mist.

Can I use Marine Mist instead of Ion Blue?

The same difference applies the other way round: Marine Mist is more saturated, warmer.

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.