ΔE 12.2, fair: the same colour family, but not a straight swap. Light Phthalo Blue is a little lighter, more saturated than Blue Horror. They are different kinds of paint: Citadel Blue Horror 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 12). Light Phthalo Blue is a little lighter, more saturated than Blue Horror. They are different kinds of paint.
The same difference applies the other way round: Blue Horror is a little darker, more muted.
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 Blue Horror on the colour wheel See Light Phthalo Blue on the colour wheel
All matches: Blue Horror equivalents · Light Phthalo Blue equivalents