Spring Green vs Fern Green

How close are they?

ΔE 20.0, loose: different enough that you should pick on purpose. Fern Green is a little lighter, much more muted than Spring Green.

Can I use Fern Green instead of Spring Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Fern Green is a little lighter, much more muted than Spring Green.

Can I use Spring Green instead of Fern Green?

The same difference applies the other way round: Spring Green is a little darker, much more saturated.

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.