Kislev Flesh vs Red Flesh

How close are they?

ΔE 19.1, loose: different enough that you should pick on purpose. Red Flesh is noticeably darker, more saturated, cooler than Kislev Flesh.

Can I use Red Flesh instead of Kislev Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Red Flesh is noticeably darker, more saturated, cooler than Kislev Flesh.

Can I use Kislev Flesh instead of Red Flesh?

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