ΔE 13.5, fair: the same colour family, but not a straight swap. Black Legion is much more muted than Night Blue INK. They are different kinds of paint: AK Interactive Night Blue INK is an ink, glaze or transparent paint and Citadel Black Legion is a one-coat contrast-style paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Black Legion is much more muted than Night Blue INK. They are different kinds of paint.
The same difference applies the other way round: Night Blue INK 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 Night Blue INK on the colour wheel See Black Legion on the colour wheel
All matches: Night Blue INK equivalents · Black Legion equivalents