ΔE 14.1, fair: the same colour family, but not a straight swap. Primary Cyan is noticeably lighter than Ionic Blue. They are different kinds of paint: Army Painter Ionic Blue is an opaque base/layer paint and Golden Primary Cyan 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 14). Primary Cyan is noticeably lighter than Ionic Blue. They are different kinds of paint.
The same difference applies the other way round: Ionic Blue is noticeably darker.
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 Ionic Blue on the colour wheel See Primary Cyan on the colour wheel
All matches: Ionic Blue equivalents · Primary Cyan equivalents