ΔE 9.8, close: similar, with a visible difference side by side. IJN Black Green is a little darker, more saturated than Dark Warm Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). IJN Black Green is a little darker, more saturated than Dark Warm Grey.
The same difference applies the other way round: Dark Warm Grey is a little lighter, more muted.
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 Dark Warm Grey on the colour wheel See IJN Black Green on the colour wheel
All matches: Dark Warm Grey equivalents · IJN Black Green equivalents