ΔE 10.7, fair: the same colour family, but not a straight swap. Tenebris Blue is noticeably darker than Alpha Blue. They are different kinds of paint: Army Painter Alpha Blue is an opaque base/layer paint and Green Stuff World Tenebris Blue is an ink, glaze or transparent 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 11). Tenebris Blue is noticeably darker than Alpha Blue. They are different kinds of paint.
The same difference applies the other way round: Alpha Blue is noticeably 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 Alpha Blue on the colour wheel See Tenebris Blue on the colour wheel
All matches: Alpha Blue equivalents · Tenebris Blue equivalents