Tallarn Sand vs Yellow Ochre

How close are they?

ΔE 23.2, loose: different enough that you should pick on purpose. Yellow Ochre is noticeably lighter, much more saturated than Tallarn Sand.

Can I use Yellow Ochre instead of Tallarn Sand?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Yellow Ochre is noticeably lighter, much more saturated than Tallarn Sand.

Can I use Tallarn Sand instead of Yellow Ochre?

The same difference applies the other way round: Tallarn Sand is noticeably darker, 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.