ΔE 13.4, fair: the same colour family, but not a straight swap. Blue Ink is noticeably lighter, more muted, cooler than Periwinkle Purple. They are different kinds of paint: Army Painter Periwinkle Purple is a one-coat contrast-style paint and Formula P3 Blue 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). Blue Ink is noticeably lighter, more muted, cooler than Periwinkle Purple. They are different kinds of paint.
The same difference applies the other way round: Periwinkle Purple is noticeably darker, more saturated, 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 Periwinkle Purple on the colour wheel See Blue Ink on the colour wheel
All matches: Periwinkle Purple equivalents · Blue Ink equivalents