ΔE 14.4, fair: the same colour family, but not a straight swap. Ultramarines Blue is noticeably darker, more saturated, cooler than Periwinkle Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Ultramarines Blue is noticeably darker, more saturated, cooler than Periwinkle Purple.
The same difference applies the other way round: Periwinkle 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 Periwinkle Purple on the colour wheel See Ultramarines Blue on the colour wheel
All matches: Periwinkle Purple equivalents · Ultramarines Blue equivalents