ΔE 6.8, close: similar, with a visible difference side by side. Fern Green is a little darker, cooler than Ardennes Green.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Fern Green is a little darker, cooler than Ardennes Green.
The same difference applies the other way round: Ardennes Green is a little lighter, 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 Ardennes Green on the colour wheel See Fern Green on the colour wheel
All matches: Ardennes Green equivalents · Fern Green equivalents