ΔE 10.2, fair: the same colour family, but not a straight swap. Ultramarine Blue is a little darker, more muted, cooler than Violet.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Ultramarine Blue is a little darker, more muted, cooler than Violet.
The same difference applies the other way round: Violet is a little lighter, more saturated, 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 Violet on the colour wheel See Ultramarine Blue on the colour wheel
All matches: Violet equivalents · Ultramarine Blue equivalents