ΔE 12.8, fair: the same colour family, but not a straight swap. Light Phthalo Green is noticeably lighter, cooler than Leviathan Light. They are different kinds of paint: Army Painter Leviathan Light is an opaque base/layer paint and Golden Light Phthalo Green 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 13). Light Phthalo Green is noticeably lighter, cooler than Leviathan Light. They are different kinds of paint.
The same difference applies the other way round: Leviathan Light is noticeably 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 Leviathan Light on the colour wheel See Light Phthalo Green on the colour wheel
All matches: Leviathan Light equivalents · Light Phthalo Green equivalents