Elysian Green vs Putrid Green

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Putrid Green is a little darker, more muted than Elysian Green.

Can I use Putrid Green instead of Elysian Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Putrid Green is a little darker, more muted than Elysian Green.

Can I use Elysian Green instead of Putrid Green?

The same difference applies the other way round: Elysian Green is a little lighter, 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.