Turnbull Turquoise vs Turquoise Ghost

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Turquoise Ghost is more saturated, warmer than Turnbull Turquoise.

Can I use Turquoise Ghost instead of Turnbull Turquoise?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Turquoise Ghost is more saturated, warmer than Turnbull Turquoise.

Can I use Turnbull Turquoise instead of Turquoise Ghost?

The same difference applies the other way round: Turnbull Turquoise is 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.