Poisonous Cloud vs Moldy Ochre

How close are they?

ΔE 25.2, loose: different enough that you should pick on purpose. Moldy Ochre is noticeably darker, more muted, warmer than Poisonous Cloud.

Can I use Moldy Ochre instead of Poisonous Cloud?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Moldy Ochre is noticeably darker, more muted, warmer than Poisonous Cloud.

Can I use Poisonous Cloud instead of Moldy Ochre?

The same difference applies the other way round: Poisonous Cloud 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.