Turquoise Blue vs Abyssal Blue

How close are they?

ΔE 6.6, close: similar, with a visible difference side by side. Abyssal Blue is a little darker than Turquoise Blue.

Can I use Abyssal Blue instead of Turquoise Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Abyssal Blue is a little darker than Turquoise Blue.

Can I use Turquoise Blue instead of Abyssal Blue?

The same difference applies the other way round: Turquoise Blue is a little lighter.

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.