Elven Flesh vs Naples Yellow Hue

How close are they?

ΔE 23.1, loose: different enough that you should pick on purpose. Naples Yellow Hue is much more saturated, cooler than Elven Flesh.

Can I use Naples Yellow Hue instead of Elven Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Naples Yellow Hue is much more saturated, cooler than Elven Flesh.

Can I use Elven Flesh instead of Naples Yellow Hue?

The same difference applies the other way round: Elven Flesh is much 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.