ΔE 6.4, close: similar, with a visible difference side by side. N3 Neutral Gray is a little lighter than Grimdark Shadow. They are different kinds of paint: Army Painter Grimdark Shadow is a wash/shade and Golden N3 Neutral Gray is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). N3 Neutral Gray is a little lighter than Grimdark Shadow. They are different kinds of paint.
The same difference applies the other way round: Grimdark Shadow is a little darker.
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 Grimdark Shadow on the colour wheel See N3 Neutral Gray on the colour wheel
All matches: Grimdark Shadow equivalents · N3 Neutral Gray equivalents