Emperor's Children vs Lilac Purple

How close are they?

ΔE 21.7, loose: different enough that you should pick on purpose. Lilac Purple is a little darker, cooler than Emperor's Children.

Can I use Lilac Purple instead of Emperor's Children?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Lilac Purple is a little darker, cooler than Emperor's Children.

Can I use Emperor's Children instead of Lilac Purple?

The same difference applies the other way round: Emperor's Children 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.