ΔE 6.3, close: similar, with a visible difference side by side. Ink Blue is a little lighter, cooler than Drakenhof Nightshade. They are different kinds of paint: Citadel Drakenhof Nightshade is a wash/shade and Vallejo Ink Blue 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). Ink Blue is a little lighter, cooler than Drakenhof Nightshade. They are different kinds of paint.
The same difference applies the other way round: Drakenhof Nightshade is a little darker, warmer.
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 Drakenhof Nightshade on the colour wheel See Ink Blue on the colour wheel
All matches: Drakenhof Nightshade equivalents · Ink Blue equivalents