Eternal Hunt vs Gnarls Green

How close are they?

ΔE 30.4, loose: different enough that you should pick on purpose. Gnarls Green is noticeably darker, much more muted than Eternal Hunt.

Can I use Gnarls Green instead of Eternal Hunt?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Gnarls Green is noticeably darker, much more muted than Eternal Hunt.

Can I use Eternal Hunt instead of Gnarls Green?

The same difference applies the other way round: Eternal Hunt is noticeably lighter, 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.