ΔE 17.8, loose: different enough that you should pick on purpose. Ultramarine Blue is more saturated, cooler than Lavender.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Ultramarine Blue is more saturated, cooler than Lavender.
The same difference applies the other way round: Lavender is 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 Lavender on the colour wheel See Ultramarine Blue on the colour wheel
All matches: Lavender equivalents · Ultramarine Blue equivalents