Dark Blue Black vs Greasy Black

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Greasy Black is a little lighter, much more muted than Dark Blue Black.

Can I use Greasy Black instead of Dark Blue Black?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Greasy Black is a little lighter, much more muted than Dark Blue Black.

Can I use Dark Blue Black instead of Greasy Black?

The same difference applies the other way round: Dark Blue Black is a little darker, 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.