Necromancer Cloak vs Dark Sea Grey

How close are they?

ΔE 8.0, close: similar, with a visible difference side by side. Dark Sea Grey is a little lighter, more muted than Necromancer Cloak.

Can I use Dark Sea Grey instead of Necromancer Cloak?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Dark Sea Grey is a little lighter, more muted than Necromancer Cloak.

Can I use Necromancer Cloak instead of Dark Sea Grey?

The same difference applies the other way round: Necromancer Cloak is a little darker, more saturated.

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.