Skink Blue vs Arcane Blue

How close are they?

ΔE 26.7, loose: different enough that you should pick on purpose. Arcane Blue is noticeably lighter, warmer than Skink Blue.

Can I use Arcane Blue instead of Skink Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Arcane Blue is noticeably lighter, warmer than Skink Blue.

Can I use Skink Blue instead of Arcane Blue?

The same difference applies the other way round: Skink Blue 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.