ΔE 6.4, close: similar, with a visible difference side by side. Dark Grey Blue is a little lighter than RLM 66 (1938).
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Dark Grey Blue is a little lighter than RLM 66 (1938).
The same difference applies the other way round: RLM 66 (1938) is a little darker.
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 RLM 66 (1938) on the colour wheel See Dark Grey Blue on the colour wheel
All matches: RLM 66 (1938) equivalents · Dark Grey Blue equivalents