ΔE 9.8, close: similar, with a visible difference side by side. Dark DAK Green is a little lighter, cooler than RAL 6003 Olivgrün opt.2.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Dark DAK Green is a little lighter, cooler than RAL 6003 Olivgrün opt.2.
The same difference applies the other way round: RAL 6003 Olivgrün opt.2 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 RAL 6003 Olivgrün opt.2 on the colour wheel See Dark DAK Green on the colour wheel
All matches: RAL 6003 Olivgrün opt.2 equivalents · Dark DAK Green equivalents