ΔE 8.3, close: similar, with a visible difference side by side. Regiment Grey is more muted than Russian Blue.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Regiment Grey is more muted than Russian Blue.
The same difference applies the other way round: Russian 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 Russian Blue on the colour wheel See Regiment Grey on the colour wheel
All matches: Russian Blue equivalents · Regiment Grey equivalents