Screaming Sun vs Plague Brown

How close are they?

ΔE 29.3, loose: different enough that you should pick on purpose. Plague Brown is noticeably darker, more muted, warmer than Screaming Sun.

Can I use Plague Brown instead of Screaming Sun?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Plague Brown is noticeably darker, more muted, warmer than Screaming Sun.

Can I use Screaming Sun instead of Plague Brown?

The same difference applies the other way round: Screaming Sun is noticeably lighter, 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.