Turquoise vs Ink Black

How close are they?

ΔE 32.1, loose: different enough that you should pick on purpose. Ink Black is noticeably darker, much more muted than Turquoise.

Can I use Ink Black instead of Turquoise?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Ink Black is noticeably darker, much more muted than Turquoise.

Can I use Turquoise instead of Ink Black?

The same difference applies the other way round: Turquoise is noticeably lighter, 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.