Rotten Pus vs Dreadnought Yellow

How close are they?

ΔE 30.0, loose: different enough that you should pick on purpose. Dreadnought Yellow is noticeably darker, much more muted, warmer than Rotten Pus.

Can I use Dreadnought Yellow instead of Rotten Pus?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Dreadnought Yellow is noticeably darker, much more muted, warmer than Rotten Pus.

Can I use Rotten Pus instead of Dreadnought Yellow?

The same difference applies the other way round: Rotten Pus is noticeably 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.