ΔE 5.1, very close: most people won’t see a difference side by side. Black Grey RLM66 is a little darker than RAF Extra Dark Sea Grey BS381C/640.
Yes, for most jobs. Very close match (ΔE 5). Black Grey RLM66 is a little darker than RAF Extra Dark Sea Grey BS381C/640.
The same difference applies the other way round: RAF Extra Dark Sea Grey BS381C/640 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.
See RAF Extra Dark Sea Grey BS381C/640 on the colour wheel See Black Grey RLM66 on the colour wheel
All matches: RAF Extra Dark Sea Grey BS381C/640 equivalents · Black Grey RLM66 equivalents