ΔE 6.1, close: similar, with a visible difference side by side. Umber Ink is more saturated than Matt Black Primer. They are different kinds of paint: Army Painter Matt Black Primer is a technical paint or medium and Nocturna Models Umber Ink is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Umber Ink is more saturated than Matt Black Primer. They are different kinds of paint.
The same difference applies the other way round: Matt Black Primer is 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 Matt Black Primer on the colour wheel See Umber Ink on the colour wheel
All matches: Matt Black Primer equivalents · Umber Ink equivalents