Gangrene vs Fern Green

How close are they?

ΔE 15.8, loose: different enough that you should pick on purpose. Fern Green is a little lighter, more muted, cooler than Gangrene.

Can I use Fern Green instead of Gangrene?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Fern Green is a little lighter, more muted, cooler than Gangrene.

Can I use Gangrene instead of Fern Green?

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