ΔE 8.8, close: similar, with a visible difference side by side. Turquoise Ink is a little darker, more muted, warmer than Nighthaunt Gloom. They are different kinds of paint: Citadel Nighthaunt Gloom is a one-coat contrast-style paint and Formula P3 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 9). Turquoise Ink is a little darker, more muted, warmer than Nighthaunt Gloom. They are different kinds of paint.
The same difference applies the other way round: Nighthaunt Gloom is a little lighter, more saturated, cooler.
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 Nighthaunt Gloom on the colour wheel See Turquoise Ink on the colour wheel
All matches: Nighthaunt Gloom equivalents · Turquoise Ink equivalents