ΔE 13.6, fair: the same colour family, but not a straight swap. Green Yellow is a little darker, warmer than Fallen Grass.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Green Yellow is a little darker, warmer than Fallen Grass.
The same difference applies the other way round: Fallen Grass is a little lighter, cooler.
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 Fallen Grass on the colour wheel See Green Yellow on the colour wheel
All matches: Fallen Grass equivalents · Green Yellow equivalents