Doom Death Black vs Midnight Purple

How close are they?

ΔE 23.3, loose: different enough that you should pick on purpose. Midnight Purple is noticeably darker, much more saturated than Doom Death Black.

Can I use Midnight Purple instead of Doom Death Black?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Midnight Purple is noticeably darker, much more saturated than Doom Death Black.

Can I use Doom Death Black instead of Midnight Purple?

The same difference applies the other way round: Doom Death Black 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.