Aqua Turquoise vs Hydra Turquoise

How close are they?

ΔE 9.9, close: similar, with a visible difference side by side. Hydra Turquoise is cooler than Aqua Turquoise.

Can I use Hydra Turquoise instead of Aqua Turquoise?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Hydra Turquoise is cooler than Aqua Turquoise.

Can I use Aqua Turquoise instead of Hydra Turquoise?

The same difference applies the other way round: Aqua Turquoise is 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.