Hydra Turquoise vs Coal Black

How close are they?

ΔE 21.5, loose: different enough that you should pick on purpose. Coal Black is noticeably darker, more muted than Hydra Turquoise.

Can I use Coal Black instead of Hydra Turquoise?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Coal Black is noticeably darker, more muted than Hydra Turquoise.

Can I use Hydra Turquoise instead of Coal Black?

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