Disgusting Slime vs Rotten Green

How close are they?

ΔE 22.7, loose: different enough that you should pick on purpose. Rotten Green is noticeably darker, much more muted than Disgusting Slime.

Can I use Rotten Green instead of Disgusting Slime?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Rotten Green is noticeably darker, much more muted than Disgusting Slime.

Can I use Disgusting Slime instead of Rotten Green?

The same difference applies the other way round: Disgusting Slime 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.