Lemon Yellow vs Fairy Flesh

How close are they?

ΔE 24.3, loose: different enough that you should pick on purpose. Fairy Flesh is noticeably darker, more muted, warmer than Lemon Yellow.

Can I use Fairy Flesh instead of Lemon Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Fairy Flesh is noticeably darker, more muted, warmer than Lemon Yellow.

Can I use Lemon Yellow instead of Fairy Flesh?

The same difference applies the other way round: Lemon Yellow is noticeably lighter, more saturated, cooler.

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.