Air Superiority Blue vs Turquoise

How close are they?

ΔE 17.8, loose: different enough that you should pick on purpose. Turquoise is noticeably lighter, more saturated, cooler than Air Superiority Blue.

Can I use Turquoise instead of Air Superiority Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Turquoise is noticeably lighter, more saturated, cooler than Air Superiority Blue.

Can I use Air Superiority Blue instead of Turquoise?

The same difference applies the other way round: Air Superiority Blue is noticeably darker, more muted, 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.