Emerald Forest vs Park Green

How close are they?

ΔE 21.3, loose: different enough that you should pick on purpose. Park Green is a little darker, more muted, cooler than Emerald Forest.

Can I use Park Green instead of Emerald Forest?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Park Green is a little darker, more muted, cooler than Emerald Forest.

Can I use Emerald Forest instead of Park Green?

The same difference applies the other way round: Emerald Forest is a little lighter, 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.