ΔE 13.6, fair: the same colour family, but not a straight swap. Green is a little darker, more saturated, cooler than Ork Flesh. They are different kinds of paint: Citadel Ork Flesh is a one-coat contrast-style paint and Green Stuff World 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 14). Green is a little darker, more saturated, cooler than Ork Flesh. They are different kinds of paint.
The same difference applies the other way round: Ork Flesh is a little lighter, more muted, 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 Ork Flesh on the colour wheel See Green on the colour wheel
All matches: Ork Flesh equivalents · Green equivalents