IJN Ash Grey vs Necrotic Flesh

How close are they?

ΔE 7.6, close: similar, with a visible difference side by side. Necrotic Flesh is a little darker, cooler than IJN Ash Grey.

Can I use Necrotic Flesh instead of IJN Ash Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Necrotic Flesh is a little darker, cooler than IJN Ash Grey.

Can I use IJN Ash Grey instead of Necrotic Flesh?

The same difference applies the other way round: IJN Ash Grey is a little lighter, warmer.

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.