Mythril Blade vs Hydra Turquoise

How close are they?

ΔE 23.0, loose: different enough that you should pick on purpose. Hydra Turquoise is a little lighter, much more saturated than Mythril Blade.

Can I use Hydra Turquoise instead of Mythril Blade?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Hydra Turquoise is a little lighter, much more saturated than Mythril Blade.

Can I use Mythril Blade instead of Hydra Turquoise?

The same difference applies the other way round: Mythril Blade is a little darker, 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.