ΔE 9.5, close: similar, with a visible difference side by side. Desert Tan is a little lighter, warmer than IJN Ash Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Desert Tan is a little lighter, warmer than IJN Ash Grey.
The same difference applies the other way round: IJN Ash Grey is a little darker, 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 IJN Ash Grey on the colour wheel See Desert Tan on the colour wheel
All matches: IJN Ash Grey equivalents · Desert Tan equivalents