ΔE 8.4, close: similar, with a visible difference side by side. Turquoise Ink is more saturated than The Darkness. They are different kinds of paint: Army Painter The Darkness is an opaque base/layer paint and Nocturna Models Turquoise 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 8). Turquoise Ink is more saturated than The Darkness. They are different kinds of paint.
The same difference applies the other way round: The Darkness 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 The Darkness on the colour wheel See Turquoise Ink on the colour wheel
All matches: The Darkness equivalents · Turquoise Ink equivalents