Dechala Lilac vs Pale Indigo

How close are they?

ΔE 24.2, loose: different enough that you should pick on purpose. Pale Indigo is noticeably darker, cooler than Dechala Lilac.

Can I use Pale Indigo instead of Dechala Lilac?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Pale Indigo is noticeably darker, cooler than Dechala Lilac.

Can I use Dechala Lilac instead of Pale Indigo?

The same difference applies the other way round: Dechala Lilac is noticeably lighter, 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.