Bright Sapphire vs Turquoise

How close are they?

ΔE 24.2, loose: different enough that you should pick on purpose. Turquoise is noticeably darker, more saturated, warmer than Bright Sapphire.

Can I use Turquoise instead of Bright Sapphire?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Turquoise is noticeably darker, more saturated, warmer than Bright Sapphire.

Can I use Bright Sapphire instead of Turquoise?

The same difference applies the other way round: Bright Sapphire is noticeably lighter, 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.