ΔE 14.8, fair: the same colour family, but not a straight swap. Blueberry is noticeably lighter, more muted, warmer than Ultramarine.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Blueberry is noticeably lighter, more muted, warmer than Ultramarine.
The same difference applies the other way round: Ultramarine is noticeably darker, 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 Ultramarine on the colour wheel See Blueberry on the colour wheel
All matches: Ultramarine equivalents · Blueberry equivalents