Ochre Clay vs Warm Yellow

How close are they?

ΔE 21.4, loose: different enough that you should pick on purpose. Warm Yellow is noticeably lighter, much more saturated, warmer than Ochre Clay.

Can I use Warm Yellow instead of Ochre Clay?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Warm Yellow is noticeably lighter, much more saturated, warmer than Ochre Clay.

Can I use Ochre Clay instead of Warm Yellow?

The same difference applies the other way round: Ochre Clay is noticeably darker, much more muted, 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.