ΔE 6.8, close: similar, with a visible difference side by side. Army Green is a little lighter than Dunkelgrün RLM 81.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Army Green is a little lighter than Dunkelgrün RLM 81.
The same difference applies the other way round: Dunkelgrün RLM 81 is a little darker.
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 Dunkelgrün RLM 81 on the colour wheel See Army Green on the colour wheel
All matches: Dunkelgrün RLM 81 equivalents · Army Green equivalents