ΔE 12.0, fair: the same colour family, but not a straight swap. Trooper White is noticeably lighter than Pallid Wych Flesh.
Can I use Trooper White instead of Pallid Wych Flesh?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Trooper White is noticeably lighter than Pallid Wych Flesh.
Can I use Pallid Wych Flesh instead of Trooper White?
The same difference applies the other way round: Pallid Wych Flesh is noticeably 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.