ΔE 12.8, fair: the same colour family, but not a straight swap. Blue is noticeably lighter, warmer than Ultramar Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Blue is noticeably lighter, warmer than Ultramar Blue.
The same difference applies the other way round: Ultramar Blue is noticeably darker, 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 Ultramar Blue on the colour wheel See Blue on the colour wheel
All matches: Ultramar Blue equivalents · Blue equivalents