ΔE 14.8, fair: the same colour family, but not a straight swap. Light Phthalo Blue is a little lighter, cooler than Marine Mist. They are different kinds of paint: Army Painter Marine Mist 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 a little lighter, cooler than Marine Mist. They are different kinds of paint.
The same difference applies the other way round: Marine Mist is a little darker, 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 Marine Mist on the colour wheel See Light Phthalo Blue on the colour wheel
All matches: Marine Mist equivalents · Light Phthalo Blue equivalents