Hydra Turquoise vs Cobalt Turquois

How close are they?

ΔE 20.2, loose: different enough that you should pick on purpose. Cobalt Turquois is noticeably darker, more muted, cooler than Hydra Turquoise.

Can I use Cobalt Turquois instead of Hydra Turquoise?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Cobalt Turquois is noticeably darker, more muted, cooler than Hydra Turquoise.

Can I use Hydra Turquoise instead of Cobalt Turquois?

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

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.