Ducat Blue vs Magic Blue

How close are they?

ΔE 20.5, loose: different enough that you should pick on purpose. Magic Blue is noticeably darker, more saturated, warmer than Ducat Blue.

Can I use Magic Blue instead of Ducat Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Magic Blue is noticeably darker, more saturated, warmer than Ducat Blue.

Can I use Ducat Blue instead of Magic Blue?

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