ΔE 13.4, fair: the same colour family, but not a straight swap. Flat Flesh is noticeably darker than Radiant Flesh.
✓ AK 3rd Generation equivalence chart lists these two as equivalents.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Flat Flesh is noticeably darker than Radiant Flesh.
The same difference applies the other way round: Radiant 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.
See Radiant Flesh on the colour wheel See Flat Flesh on the colour wheel
All matches: Radiant Flesh equivalents · Flat Flesh equivalents