ΔE 22.6, loose: different enough that you should pick on purpose. Mystic Blue is noticeably darker, more saturated, cooler than Morrow Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Mystic Blue is noticeably darker, more saturated, cooler than Morrow Purple.
The same difference applies the other way round: Morrow Purple is noticeably lighter, more muted, warmer.
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 Morrow Purple on the colour wheel See Mystic Blue on the colour wheel
All matches: Morrow Purple equivalents · Mystic Blue equivalents