Fey Pink vs Dechala Lilac

How close are they?

ΔE 18.7, loose: different enough that you should pick on purpose. Dechala Lilac is a little darker, cooler than Fey Pink.

Can I use Dechala Lilac instead of Fey Pink?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Dechala Lilac is a little darker, cooler than Fey Pink.

Can I use Fey Pink instead of Dechala Lilac?

The same difference applies the other way round: Fey Pink is a little 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.