ΔE 8.5, close: similar, with a visible difference side by side. IJN Black Green is a little lighter, more muted, warmer than RLM 80 Olive Green.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). IJN Black Green is a little lighter, more muted, warmer than RLM 80 Olive Green.
The same difference applies the other way round: RLM 80 Olive Green is a little darker, more saturated, cooler.
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 RLM 80 Olive Green on the colour wheel See IJN Black Green on the colour wheel
All matches: RLM 80 Olive Green equivalents · IJN Black Green equivalents