Pastel Yellow vs Seraphim Flesh

How close are they?

ΔE 65.0, loose: different enough that you should pick on purpose. Seraphim Flesh is noticeably darker, much more muted, warmer than Pastel Yellow.

Can I use Seraphim Flesh instead of Pastel Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 65). Seraphim Flesh is noticeably darker, much more muted, warmer than Pastel Yellow.

Can I use Pastel Yellow instead of Seraphim Flesh?

The same difference applies the other way round: Pastel Yellow is noticeably lighter, 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.