ΔE 12.8, fair: the same colour family, but not a straight swap. Tan Flesh is noticeably darker than Kislev Flesh.
Can I use Tan Flesh instead of Kislev Flesh?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Tan Flesh is noticeably darker than Kislev Flesh.
Can I use Kislev Flesh instead of Tan Flesh?
The same difference applies the other way round: Kislev Flesh is noticeably lighter.
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.