ΔE 10.2, fair: the same colour family, but not a straight swap. Malignant Green is a little darker, more saturated than Ghostly Green. They are different kinds of paint: AMMO by Mig Ghostly Green is an opaque base/layer paint and Army Painter Malignant Green is a one-coat contrast-style 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 10). Malignant Green is a little darker, more saturated than Ghostly Green. They are different kinds of paint.
The same difference applies the other way round: Ghostly Green is a little lighter, 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 Ghostly Green on the colour wheel See Malignant Green on the colour wheel
All matches: Ghostly Green equivalents · Malignant Green equivalents