ΔE 10.5, fair: the same colour family, but not a straight swap. Guardian Green is more muted, cooler than Fern Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Guardian Green is more muted, cooler than Fern Green.
The same difference applies the other way round: Fern Green is 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 Fern Green on the colour wheel See Guardian Green on the colour wheel
All matches: Fern Green equivalents · Guardian Green equivalents