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