Washable Sand vs T'au Light Ochre

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. T'au Light Ochre is noticeably darker, more saturated, warmer than Washable Sand.

Can I use T'au Light Ochre instead of Washable Sand?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). T'au Light Ochre is noticeably darker, more saturated, warmer than Washable Sand.

Can I use Washable Sand instead of T'au Light Ochre?

The same difference applies the other way round: Washable Sand is noticeably lighter, 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.