Trollblood Highlight vs Elfic Flesh

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Elfic Flesh is noticeably lighter, warmer than Trollblood Highlight.

Can I use Elfic Flesh instead of Trollblood Highlight?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Elfic Flesh is noticeably lighter, warmer than Trollblood Highlight.

Can I use Trollblood Highlight instead of Elfic Flesh?

The same difference applies the other way round: Trollblood Highlight is noticeably darker, 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.