ΔE 6.6, close: similar, with a visible difference side by side. Night Blue is a little darker than RAL 7021 Dunkelgrau.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Night Blue is a little darker than RAL 7021 Dunkelgrau.
The same difference applies the other way round: RAL 7021 Dunkelgrau 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 RAL 7021 Dunkelgrau on the colour wheel See Night Blue on the colour wheel
All matches: RAL 7021 Dunkelgrau equivalents · Night Blue equivalents