Frog Green vs Emerald Forest

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Emerald Forest is a little darker, more saturated, cooler than Frog Green.

Can I use Emerald Forest instead of Frog Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Emerald Forest is a little darker, more saturated, cooler than Frog Green.

Can I use Frog Green instead of Emerald Forest?

The same difference applies the other way round: Frog Green is a little lighter, more muted, 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.