Cobalt Blue vs Death Metal

How close are they?

ΔE 21.9, loose: different enough that you should pick on purpose. Death Metal is noticeably lighter, much more muted than Cobalt Blue.

Can I use Death Metal instead of Cobalt Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Death Metal is noticeably lighter, much more muted than Cobalt Blue.

Can I use Cobalt Blue instead of Death Metal?

The same difference applies the other way round: Cobalt Blue is noticeably 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.