ΔE 6.6, close: similar, with a visible difference side by side. Russ Grey is more muted than Marine Blue. They are different kinds of paint: AMMO by Mig Marine Blue is an ink, glaze or transparent paint and Citadel Russ Grey is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Russ Grey is more muted than Marine Blue. They are different kinds of paint.
The same difference applies the other way round: Marine Blue is 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.
See Marine Blue on the colour wheel See Russ Grey on the colour wheel
All matches: Marine Blue equivalents · Russ Grey equivalents