Glitter Green vs Forrest Flux

How close are they?

ΔE 19.1, loose: different enough that you should pick on purpose. Forrest Flux is a little lighter, much more muted than Glitter Green.

Can I use Forrest Flux instead of Glitter Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Forrest Flux is a little lighter, much more muted than Glitter Green.

Can I use Glitter Green instead of Forrest Flux?

The same difference applies the other way round: Glitter 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.