ΔE 15.2, loose: different enough that you should pick on purpose. Night Blue is noticeably darker, more muted than Steel Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Night Blue is noticeably darker, more muted than Steel Grey.
The same difference applies the other way round: Steel Grey is noticeably lighter, more saturated.
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 Steel Grey on the colour wheel See Night Blue on the colour wheel
All matches: Steel Grey equivalents · Night Blue equivalents