ΔE 51.9, loose: different enough that you should pick on purpose. Forest Green is noticeably darker, much more muted, cooler than Shamrock Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 52). Forest Green is noticeably darker, much more muted, cooler than Shamrock Green.
The same difference applies the other way round: Shamrock Green 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 Shamrock Green on the colour wheel See Forest Green on the colour wheel
All matches: Shamrock Green equivalents · Forest Green equivalents