Black Forest Green vs Emerald

How close are they?

ΔE 16.4, loose: different enough that you should pick on purpose. Emerald is noticeably lighter, more saturated than Black Forest Green.

Can I use Emerald instead of Black Forest Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Emerald is noticeably lighter, more saturated than Black Forest Green.

Can I use Black Forest Green instead of Emerald?

The same difference applies the other way round: Black Forest Green is noticeably darker, more muted.

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.