Dark Aluminium vs Cobalt Metal

How close are they?

ΔE 19.6, loose: different enough that you should pick on purpose. Cobalt Metal is noticeably darker, much more saturated than Dark Aluminium.

Can I use Cobalt Metal instead of Dark Aluminium?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Cobalt Metal is noticeably darker, much more saturated than Dark Aluminium.

Can I use Dark Aluminium instead of Cobalt Metal?

The same difference applies the other way round: Dark Aluminium is noticeably lighter, much more muted.

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.