ΔE 6.6, close: similar, with a visible difference side by side. Alpha Blue is a little lighter, cooler than Matt Ultra Blue. They are different kinds of paint: AMMO by Mig Matt Ultra Blue is an ink, glaze or transparent paint and Army Painter Alpha Blue is an opaque base/layer 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 7). Alpha Blue is a little lighter, cooler than Matt Ultra Blue. They are different kinds of paint.
The same difference applies the other way round: Matt Ultra Blue 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 Matt Ultra Blue on the colour wheel See Alpha Blue on the colour wheel
All matches: Matt Ultra Blue equivalents · Alpha Blue equivalents