ΔE 6.6, close: similar, with a visible difference side by side. IJN Medium Grey is a little darker than IJA Grey Green.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). IJN Medium Grey is a little darker than IJA Grey Green.
The same difference applies the other way round: IJA Grey Green is a little lighter.
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 IJA Grey Green on the colour wheel See IJN Medium Grey on the colour wheel
All matches: IJA Grey Green equivalents · IJN Medium Grey equivalents