ΔE 11.7, fair: the same colour family, but not a straight swap. Transparent Cold Green is a little lighter, more saturated than Waaagh! Flesh. They are different kinds of paint: Citadel Waaagh! Flesh is an opaque base/layer paint and Green Stuff World Transparent Cold 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). Transparent Cold Green is a little lighter, more saturated than Waaagh! Flesh. They are different kinds of paint.
The same difference applies the other way round: Waaagh! Flesh 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 Waaagh! Flesh on the colour wheel See Transparent Cold Green on the colour wheel
All matches: Waaagh! Flesh equivalents · Transparent Cold Green equivalents