Bright Yellow Ochre vs Leather Brown

How close are they?

ΔE 18.0, loose: different enough that you should pick on purpose. Leather Brown is noticeably darker, much more saturated than Bright Yellow Ochre.

Can I use Leather Brown instead of Bright Yellow Ochre?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Leather Brown is noticeably darker, much more saturated than Bright Yellow Ochre.

Can I use Bright Yellow Ochre instead of Leather Brown?

The same difference applies the other way round: Bright Yellow Ochre is noticeably lighter, much more muted.

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.