Yellow FS33531 vs Fairy Flesh

How close are they?

ΔE 17.9, loose: different enough that you should pick on purpose. Fairy Flesh is a little lighter, much more muted, warmer than Yellow FS33531.

Can I use Fairy Flesh instead of Yellow FS33531?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Fairy Flesh is a little lighter, much more muted, warmer than Yellow FS33531.

Can I use Yellow FS33531 instead of Fairy Flesh?

The same difference applies the other way round: Yellow FS33531 is a little darker, much 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.