Pallid Wych Flesh vs Leather White

How close are they?

ΔE 6.6, close: similar, with a visible difference side by side. Leather White is a little lighter than Pallid Wych Flesh.

Can I use Leather White instead of Pallid Wych Flesh?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Leather White is a little lighter than Pallid Wych Flesh.

Can I use Pallid Wych Flesh instead of Leather White?

The same difference applies the other way round: Pallid Wych Flesh is a little darker.

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.