ΔE 10.5, fair: the same colour family, but not a straight swap. Incubi Darkness is a little darker, cooler than Night Blue. They are different kinds of paint: AMMO by Mig Night Blue is an ink, glaze or transparent paint and Citadel Incubi Darkness is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Incubi Darkness is a little darker, cooler than Night Blue. They are different kinds of paint.
The same difference applies the other way round: Night Blue is a little lighter, 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 Night Blue on the colour wheel See Incubi Darkness on the colour wheel
All matches: Night Blue equivalents · Incubi Darkness equivalents