ΔE 10.8, fair: the same colour family, but not a straight swap. White Star is noticeably lighter than Apothecary White. They are different kinds of paint: Citadel Apothecary White is a one-coat contrast-style paint and Two Thin Coats White Star 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). White Star is noticeably lighter than Apothecary White. They are different kinds of paint.
The same difference applies the other way round: Apothecary White 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 Apothecary White on the colour wheel See White Star on the colour wheel
All matches: Apothecary White equivalents · White Star equivalents