ΔE 8.9, close: similar, with a visible difference side by side. Umber Ink is a little darker than Grim Black. They are different kinds of paint: Army Painter Grim Black is a one-coat contrast-style paint 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 9). Umber Ink is a little darker than Grim Black. They are different kinds of paint.
The same difference applies the other way round: Grim Black is a little lighter.
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 Grim Black on the colour wheel See Umber Ink on the colour wheel
All matches: Grim Black equivalents · Umber Ink equivalents