ΔE 17.9, loose: different enough that you should pick on purpose. Park Green Flat is noticeably lighter, more saturated, warmer than Dark Emerald.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Park Green Flat is noticeably lighter, more saturated, warmer than Dark Emerald.
The same difference applies the other way round: Dark Emerald is noticeably darker, more muted, 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 Emerald on the colour wheel See Park Green Flat on the colour wheel
All matches: Dark Emerald equivalents · Park Green Flat equivalents