Naggaroth Night vs Sea Blue

How close are they?

ΔE 19.6, loose: different enough that you should pick on purpose. Sea Blue is a little lighter, more muted, cooler than Naggaroth Night.

Can I use Sea Blue instead of Naggaroth Night?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Sea Blue is a little lighter, more muted, cooler than Naggaroth Night.

Can I use Naggaroth Night instead of Sea Blue?

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