Ducat Blue vs Skink Blue

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Skink Blue is noticeably darker, more muted than Ducat Blue.

Can I use Skink Blue instead of Ducat Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Skink Blue is noticeably darker, more muted than Ducat Blue.

Can I use Ducat Blue instead of Skink Blue?

The same difference applies the other way round: Ducat Blue is noticeably lighter, more saturated.

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.