Light Sand vs Pallid Wych Flesh

How close are they?

ΔE 9.8, close: similar, with a visible difference side by side. Pallid Wych Flesh is a little darker, cooler than Light Sand.

Can I use Pallid Wych Flesh instead of Light Sand?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Pallid Wych Flesh is a little darker, cooler than Light Sand.

Can I use Light Sand instead of Pallid Wych Flesh?

The same difference applies the other way round: Light Sand is a little lighter, warmer.

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.