Eternal Hunt vs Bright Green

How close are they?

ΔE 8.9, close: similar, with a visible difference side by side. Bright Green is a little lighter than Eternal Hunt.

Can I use Bright Green instead of Eternal Hunt?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Bright Green is a little lighter than Eternal Hunt.

Can I use Eternal Hunt instead of Bright Green?

The same difference applies the other way round: Eternal Hunt is a little darker.

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.