Phoenician Purple vs Permanent Violet Dark

How close are they?

ΔE 20.6, loose: different enough that you should pick on purpose. Permanent Violet Dark is much more saturated, cooler than Phoenician Purple.

Can I use Permanent Violet Dark instead of Phoenician Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Permanent Violet Dark is much more saturated, cooler than Phoenician Purple.

Can I use Phoenician Purple instead of Permanent Violet Dark?

The same difference applies the other way round: Phoenician Purple is much 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.