Alaitoc Blue vs Turquois (Phthalo)

How close are they?

ΔE 25.2, loose: different enough that you should pick on purpose. Turquois (Phthalo) is a little darker, more muted, cooler than Alaitoc Blue.

Can I use Turquois (Phthalo) instead of Alaitoc Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Turquois (Phthalo) is a little darker, more muted, cooler than Alaitoc Blue.

Can I use Alaitoc Blue instead of Turquois (Phthalo)?

The same difference applies the other way round: Alaitoc Blue is a little lighter, more saturated, 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.