ΔE 10.3, fair: the same colour family, but not a straight swap. Turquoise Ink is warmer than Runic Grey. They are different kinds of paint: Army Painter Runic Grey is a one-coat contrast-style 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 10). Turquoise Ink is warmer than Runic Grey. They are different kinds of paint.
The same difference applies the other way round: Runic Grey is 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 Runic Grey on the colour wheel See Turquoise Ink on the colour wheel
All matches: Runic Grey equivalents · Turquoise Ink equivalents