RAF Medium Sea Grey BS381C/637 vs Uniform Grey

How close are they?

ΔE 7.7, close: similar, with a visible difference side by side. Uniform Grey is a little darker than RAF Medium Sea Grey BS381C/637.

Can I use Uniform Grey instead of RAF Medium Sea Grey BS381C/637?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Uniform Grey is a little darker than RAF Medium Sea Grey BS381C/637.

Can I use RAF Medium Sea Grey BS381C/637 instead of Uniform Grey?

The same difference applies the other way round: RAF Medium Sea Grey BS381C/637 is a little lighter.

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.