Senshi Skin vs Trollblood Highlight

How close are they?

ΔE 15.8, loose: different enough that you should pick on purpose. Trollblood Highlight is a little darker, much more muted, cooler than Senshi Skin.

Can I use Trollblood Highlight instead of Senshi Skin?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Trollblood Highlight is a little darker, much more muted, cooler than Senshi Skin.

Can I use Senshi Skin instead of Trollblood Highlight?

The same difference applies the other way round: Senshi Skin is a little lighter, much more saturated, 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.