RAF Dark Sea Grey BS381C/638 vs London Grey

How close are they?

ΔE 4.5, very close: most people won’t see a difference side by side. London Grey is a little darker than RAF Dark Sea Grey BS381C/638.

Can I use London Grey instead of RAF Dark Sea Grey BS381C/638?

Yes, for most jobs. Very close match (ΔE 4). London Grey is a little darker than RAF Dark Sea Grey BS381C/638.

Can I use RAF Dark Sea Grey BS381C/638 instead of London Grey?

The same difference applies the other way round: RAF Dark Sea Grey BS381C/638 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.