ΔE 33.0, loose: different enough that you should pick on purpose. Dechala Lilac is a little darker, much more muted, warmer than Twilight at Gettysburg.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 33). Dechala Lilac is a little darker, much more muted, warmer than Twilight at Gettysburg.
The same difference applies the other way round: Twilight at Gettysburg is a little lighter, much 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.
See Twilight at Gettysburg on the colour wheel See Dechala Lilac on the colour wheel
All matches: Twilight at Gettysburg equivalents · Dechala Lilac equivalents