ΔE 12.6, fair: the same colour family, but not a straight swap. Atramentum Black is much more muted than Nightroot Shade.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Atramentum Black is much more muted than Nightroot Shade.
The same difference applies the other way round: Nightroot Shade is much 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.
See Nightroot Shade on the colour wheel See Atramentum Black on the colour wheel
All matches: Nightroot Shade equivalents · Atramentum Black equivalents