ΔE 11.5, fair: the same colour family, but not a straight swap. Niblet Green is a little lighter, more muted, cooler than Undergrowth Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Niblet Green is a little lighter, more muted, cooler than Undergrowth Green.
The same difference applies the other way round: Undergrowth Green is a little darker, more saturated, 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 Undergrowth Green on the colour wheel See Niblet Green on the colour wheel
All matches: Undergrowth Green equivalents · Niblet Green equivalents