ΔE 10.7, fair: the same colour family, but not a straight swap. Skink Blue is noticeably lighter than Duck Blue.
Can I use Skink Blue instead of Duck Blue?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Skink Blue is noticeably lighter than Duck Blue.
Can I use Duck Blue instead of Skink Blue?
The same difference applies the other way round: Duck Blue is noticeably darker.
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.