ΔE 6.9, close: similar, with a visible difference side by side. Flat Green is a little lighter, cooler than Olivgrün (RLM 71).
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Flat Green is a little lighter, cooler than Olivgrün (RLM 71).
The same difference applies the other way round: Olivgrün (RLM 71) is a little darker, 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 Olivgrün (RLM 71) on the colour wheel See Flat Green on the colour wheel
All matches: Olivgrün (RLM 71) equivalents · Flat Green equivalents