ΔE 18.1, loose: different enough that you should pick on purpose. Dark Prussian Blue is noticeably darker, warmer than Abyss Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Dark Prussian Blue is noticeably darker, warmer than Abyss Blue.
The same difference applies the other way round: Abyss Blue is noticeably lighter, 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 Abyss Blue on the colour wheel See Dark Prussian Blue on the colour wheel
All matches: Abyss Blue equivalents · Dark Prussian Blue equivalents