Moldy Ochre vs Plague Brown

How close are they?

ΔE 7.5, close: similar, with a visible difference side by side. Plague Brown is warmer than Moldy Ochre.

Can I use Plague Brown instead of Moldy Ochre?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Plague Brown is warmer than Moldy Ochre.

Can I use Moldy Ochre instead of Plague Brown?

The same difference applies the other way round: Moldy Ochre is 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.