ΔE 13.4, fair: the same colour family, but not a straight swap. Turquoise Ink is a little lighter, more muted, warmer than Deep Azure. They are different kinds of paint: Army Painter Deep Azure is an opaque base/layer 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.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Turquoise Ink is a little lighter, more muted, warmer than Deep Azure. They are different kinds of paint.
The same difference applies the other way round: Deep Azure is a little darker, 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 Deep Azure on the colour wheel See Turquoise Ink on the colour wheel
All matches: Deep Azure equivalents · Turquoise Ink equivalents