ΔE 41.2, loose: different enough that you should pick on purpose. Fallen Grass is noticeably darker, much more muted, cooler than Mortarion Green Clear.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 41). Fallen Grass is noticeably darker, much more muted, cooler than Mortarion Green Clear.
The same difference applies the other way round: Mortarion Green Clear is noticeably lighter, much 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 Mortarion Green Clear on the colour wheel See Fallen Grass on the colour wheel
All matches: Mortarion Green Clear equivalents · Fallen Grass equivalents