Wildling Flesh vs Khardic Flesh

How close are they?

ΔE 22.6, loose: different enough that you should pick on purpose. Khardic Flesh is noticeably darker, more saturated than Wildling Flesh.

Can I use Khardic Flesh instead of Wildling Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Khardic Flesh is noticeably darker, more saturated than Wildling Flesh.

Can I use Wildling Flesh instead of Khardic Flesh?

The same difference applies the other way round: Wildling Flesh is noticeably lighter, more muted.

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.