Ferocious Green vs Pale Green

How close are they?

ΔE 17.9, loose: different enough that you should pick on purpose. Pale Green is a little darker, much more saturated, cooler than Ferocious Green.

Can I use Pale Green instead of Ferocious Green?

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

Can I use Ferocious Green instead of Pale Green?

The same difference applies the other way round: Ferocious Green is a little lighter, much 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.