ΔE 16.2, loose: different enough that you should pick on purpose. Plague Green is much more muted, warmer than Dark Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Plague Green is much more muted, warmer than Dark Green.
The same difference applies the other way round: Dark Green is much 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 Dark Green on the colour wheel See Plague Green on the colour wheel
All matches: Dark Green equivalents · Plague Green equivalents