ΔE 16.6, loose: different enough that you should pick on purpose. Blue FS15044 is much more muted, cooler than Naggaroth Night.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Blue FS15044 is much more muted, cooler than Naggaroth Night.
The same difference applies the other way round: Naggaroth Night is much 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.
See Naggaroth Night on the colour wheel See Blue FS15044 on the colour wheel
All matches: Naggaroth Night equivalents · Blue FS15044 equivalents