ΔE 16.5, loose: different enough that you should pick on purpose. Magic Blue is a little darker, much more saturated, warmer than Seafarer Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Magic Blue is a little darker, much more saturated, warmer than Seafarer Blue.
The same difference applies the other way round: Seafarer Blue is a little lighter, much 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.
See Seafarer Blue on the colour wheel See Magic Blue on the colour wheel
All matches: Seafarer Blue equivalents · Magic Blue equivalents