Bony Matter vs Seraphim Flesh

How close are they?

ΔE 19.5, loose: different enough that you should pick on purpose. Seraphim Flesh is a little darker, much more saturated, cooler than Bony Matter.

Can I use Seraphim Flesh instead of Bony Matter?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Seraphim Flesh is a little darker, much more saturated, cooler than Bony Matter.

Can I use Bony Matter instead of Seraphim Flesh?

The same difference applies the other way round: Bony Matter is a little lighter, 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.