ΔE 32.9, loose: different enough that you should pick on purpose. Morrow Purple is noticeably lighter, much more muted, warmer than Ultramarines Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 33). Morrow Purple is noticeably lighter, much more muted, warmer than Ultramarines Blue.
The same difference applies the other way round: Ultramarines Blue is noticeably darker, much more saturated, 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 Ultramarines Blue on the colour wheel See Morrow Purple on the colour wheel
All matches: Ultramarines Blue equivalents · Morrow Purple equivalents