Twilight at Gettysburg vs Andrea Blue

How close are they?

ΔE 24.7, loose: different enough that you should pick on purpose. Andrea Blue is noticeably darker, more muted, cooler than Twilight at Gettysburg.

Can I use Andrea Blue instead of Twilight at Gettysburg?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Andrea Blue is noticeably darker, more muted, cooler than Twilight at Gettysburg.

Can I use Twilight at Gettysburg instead of Andrea Blue?

The same difference applies the other way round: Twilight at Gettysburg is noticeably lighter, more saturated, 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.