ΔE 9.8, close: similar, with a visible difference side by side. Necromancer Cloak is a little darker, cooler than Grey Shadow.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Necromancer Cloak is a little darker, cooler than Grey Shadow.
The same difference applies the other way round: Grey Shadow 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.
See Grey Shadow on the colour wheel See Necromancer Cloak on the colour wheel
All matches: Grey Shadow equivalents · Necromancer Cloak equivalents