Rotten Green vs Dark Yellow

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Dark Yellow is a little darker, much more muted, warmer than Rotten Green.

Can I use Dark Yellow instead of Rotten Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Dark Yellow is a little darker, much more muted, warmer than Rotten Green.

Can I use Rotten Green instead of Dark Yellow?

The same difference applies the other way round: Rotten Green is a little lighter, much more saturated, cooler.

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.