ΔE 20.7, loose: different enough that you should pick on purpose. Dark Green is a little darker, much more saturated, cooler than Thornwood Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Dark Green is a little darker, much more saturated, cooler than Thornwood Green.
The same difference applies the other way round: Thornwood Green is a little lighter, much more muted, warmer.
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 Thornwood Green on the colour wheel See Dark Green on the colour wheel
All matches: Thornwood Green equivalents · Dark Green equivalents