ΔE 11.9, fair: the same colour family, but not a straight swap. Flat Green is noticeably darker, cooler than Ardennes Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Flat Green is noticeably darker, cooler than Ardennes Green.
The same difference applies the other way round: Ardennes Green is noticeably 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 Flat Green on the colour wheel
All matches: Ardennes Green equivalents · Flat Green equivalents