ΔE 6.1, close: similar, with a visible difference side by side. Dark Sea Gray is a little darker than Necromancer Cloak.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Dark Sea Gray is a little darker than Necromancer Cloak.
The same difference applies the other way round: Necromancer Cloak is a little lighter.
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 Necromancer Cloak on the colour wheel See Dark Sea Gray on the colour wheel
All matches: Necromancer Cloak equivalents · Dark Sea Gray equivalents