Asurmen Blue vs Dark Blue Black

How close are they?

ΔE 34.5, loose: different enough that you should pick on purpose. Dark Blue Black is noticeably darker, much more muted, warmer than Asurmen Blue.

Can I use Dark Blue Black instead of Asurmen Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 35). Dark Blue Black is noticeably darker, much more muted, warmer than Asurmen Blue.

Can I use Asurmen Blue instead of Dark Blue Black?

The same difference applies the other way round: Asurmen 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.