Twilight at Gettysburg vs Orchid Light

How close are they?

ΔE 22.7, loose: different enough that you should pick on purpose. Orchid Light is a little darker, more muted, warmer than Twilight at Gettysburg.

Can I use Orchid Light instead of Twilight at Gettysburg?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Orchid Light is a little darker, more muted, warmer than Twilight at Gettysburg.

Can I use Twilight at Gettysburg instead of Orchid Light?

The same difference applies the other way round: Twilight at Gettysburg is a little lighter, 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.