ΔE 16.9, loose: different enough that you should pick on purpose. Brown Beast Ink is much more saturated than Black Templar. They are different kinds of paint: Citadel Black Templar is a one-coat contrast-style paint and Nocturna Models Brown Beast Ink is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Brown Beast Ink is much more saturated than Black Templar. They are different kinds of paint.
The same difference applies the other way round: Black Templar is much more muted.
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 Black Templar on the colour wheel See Brown Beast Ink on the colour wheel
All matches: Black Templar equivalents · Brown Beast Ink equivalents