ΔE 8.0, close: similar, with a visible difference side by side. IJN Ash Grey is a little lighter, more muted, warmer than Dark Seagray.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). IJN Ash Grey is a little lighter, more muted, warmer than Dark Seagray.
The same difference applies the other way round: Dark Seagray 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 Dark Seagray on the colour wheel See IJN Ash Grey on the colour wheel
All matches: Dark Seagray equivalents · IJN Ash Grey equivalents