Pale Indigo vs Lustful Purple

How close are they?

ΔE 21.4, loose: different enough that you should pick on purpose. Lustful Purple is noticeably lighter, more muted, warmer than Pale Indigo.

Can I use Lustful Purple instead of Pale Indigo?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Lustful Purple is noticeably lighter, more muted, warmer than Pale Indigo.

Can I use Pale Indigo instead of Lustful Purple?

The same difference applies the other way round: Pale Indigo is noticeably darker, more saturated, 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.