ΔE 14.5, fair: the same colour family, but not a straight swap. Steel Grey is noticeably darker, more muted, warmer than Nocturne Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Steel Grey is noticeably darker, more muted, warmer than Nocturne Green.
The same difference applies the other way round: Nocturne Green is noticeably lighter, more saturated, cooler.
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 Nocturne Green on the colour wheel See Steel Grey on the colour wheel
All matches: Nocturne Green equivalents · Steel Grey equivalents