ΔE 6.7, close: similar, with a visible difference side by side. Desert Olive Green is more saturated than IJN J3 Hai-iro (Grey).
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Desert Olive Green is more saturated than IJN J3 Hai-iro (Grey).
The same difference applies the other way round: IJN J3 Hai-iro (Grey) is more muted.
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 IJN J3 Hai-iro (Grey) on the colour wheel See Desert Olive Green on the colour wheel
All matches: IJN J3 Hai-iro (Grey) equivalents · Desert Olive Green equivalents