ΔE 7.0, close: similar, with a visible difference side by side. Celestra Grey is a little lighter, more saturated than RAF Medium Sea Grey BS381C/637.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Celestra Grey is a little lighter, more saturated than RAF Medium Sea Grey BS381C/637.
The same difference applies the other way round: RAF Medium Sea Grey BS381C/637 is a little darker, more muted.
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 RAF Medium Sea Grey BS381C/637 on the colour wheel See Celestra Grey on the colour wheel
All matches: RAF Medium Sea Grey BS381C/637 equivalents · Celestra Grey equivalents