Dorn Yellow vs Moldy Ochre

How close are they?

ΔE 16.2, loose: different enough that you should pick on purpose. Moldy Ochre is noticeably darker, more muted than Dorn Yellow.

Can I use Moldy Ochre instead of Dorn Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Moldy Ochre is noticeably darker, more muted than Dorn Yellow.

Can I use Dorn Yellow instead of Moldy Ochre?

The same difference applies the other way round: Dorn Yellow is noticeably lighter, more saturated.

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.