ΔE 13.7, fair: the same colour family, but not a straight swap. Jade Green is a little lighter, more saturated than Aeldari Emerald. They are different kinds of paint: Citadel Aeldari Emerald is a one-coat contrast-style paint and Reaper Jade Green is an opaque base/layer 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). Jade Green is a little lighter, more saturated than Aeldari Emerald. They are different kinds of paint.
The same difference applies the other way round: Aeldari Emerald 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 Aeldari Emerald on the colour wheel See Jade Green on the colour wheel
All matches: Aeldari Emerald equivalents · Jade Green equivalents