ΔE 12.1, fair: the same colour family, but not a straight swap. Fluor Green is a little lighter, more saturated than Feral Green. They are different kinds of paint: Army Painter Feral Green is an opaque base/layer paint and Green Stuff World Fluor 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 12). Fluor Green is a little lighter, more saturated than Feral Green. They are different kinds of paint.
The same difference applies the other way round: Feral Green 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 Feral Green on the colour wheel See Fluor Green on the colour wheel
All matches: Feral Green equivalents · Fluor Green equivalents