ΔE 14.7, fair: the same colour family, but not a straight swap. Light Phthalo Blue is noticeably lighter, more saturated, cooler than Frost Blue. They are different kinds of paint: Army Painter Frost Blue is an opaque base/layer paint and Golden Light Phthalo Blue 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 15). Light Phthalo Blue is noticeably lighter, more saturated, cooler than Frost Blue. They are different kinds of paint.
The same difference applies the other way round: Frost Blue is noticeably darker, more muted, 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 Frost Blue on the colour wheel See Light Phthalo Blue on the colour wheel
All matches: Frost Blue equivalents · Light Phthalo Blue equivalents