ΔE 20.2, loose: different enough that you should pick on purpose. Blue Black is noticeably darker, much more muted, warmer than Abyssal Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Blue Black is noticeably darker, much more muted, warmer than Abyssal Blue.
The same difference applies the other way round: Abyssal Blue is noticeably lighter, much 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 Abyssal Blue on the colour wheel See Blue Black on the colour wheel
All matches: Abyssal Blue equivalents · Blue Black equivalents