ΔE 11.3, fair: the same colour family, but not a straight swap. Light Turquois (Phthalo) is a little darker, more saturated, warmer than Nihilakh Oxide. They are different kinds of paint: Citadel Nihilakh Oxide is a technical paint or medium and Golden Light Turquois (Phthalo) is an opaque base/layer 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 11). Light Turquois (Phthalo) is a little darker, more saturated, warmer than Nihilakh Oxide. They are different kinds of paint.
The same difference applies the other way round: Nihilakh Oxide is a little lighter, more muted, 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 Nihilakh Oxide on the colour wheel See Light Turquois (Phthalo) on the colour wheel
All matches: Nihilakh Oxide equivalents · Light Turquois (Phthalo) equivalents