Sentient Turquoise vs Russian AF Blue

How close are they?

ΔE 7.3, close: similar, with a visible difference side by side. Russian AF Blue is a little lighter, more saturated than Sentient Turquoise.

Can I use Russian AF Blue instead of Sentient Turquoise?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Russian AF Blue is a little lighter, more saturated than Sentient Turquoise.

Can I use Sentient Turquoise instead of Russian AF Blue?

The same difference applies the other way round: Sentient Turquoise is a little darker, 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.