ΔE 9.9, close: similar, with a visible difference side by side. IJA Grey Green is a little darker, warmer than WWI German Grey-Green Primer.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). IJA Grey Green is a little darker, warmer than WWI German Grey-Green Primer.
The same difference applies the other way round: WWI German Grey-Green Primer is a little lighter, 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 WWI German Grey-Green Primer on the colour wheel See IJA Grey Green on the colour wheel
All matches: WWI German Grey-Green Primer equivalents · IJA Grey Green equivalents