'Jack Bone vs Elfic Flesh

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Elfic Flesh is a little lighter, much more muted, warmer than 'Jack Bone.

Can I use Elfic Flesh instead of 'Jack Bone?

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

Can I use 'Jack Bone instead of Elfic Flesh?

The same difference applies the other way round: 'Jack Bone 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.