ΔE 31.7, loose: different enough that you should pick on purpose. Forest Green is noticeably darker, more muted, warmer than Belladonna Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Forest Green is noticeably darker, more muted, warmer than Belladonna Green.
The same difference applies the other way round: Belladonna Green is noticeably lighter, more saturated, 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 Belladonna Green on the colour wheel See Forest Green on the colour wheel
All matches: Belladonna Green equivalents · Forest Green equivalents