Turquoise Blue vs Andrea Blue

How close are they?

ΔE 20.6, loose: different enough that you should pick on purpose. Andrea Blue is a little lighter, much more saturated, warmer than Turquoise Blue.

Can I use Andrea Blue instead of Turquoise Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Andrea Blue is a little lighter, much more saturated, warmer than Turquoise Blue.

Can I use Turquoise Blue instead of Andrea Blue?

The same difference applies the other way round: Turquoise Blue is a little darker, much more muted, cooler.

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.