Twilight Sky vs Navy Blue

How close are they?

ΔE 18.0, loose: different enough that you should pick on purpose. Navy Blue is a little darker, more saturated, warmer than Twilight Sky.

Can I use Navy Blue instead of Twilight Sky?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Navy Blue is a little darker, more saturated, warmer than Twilight Sky.

Can I use Twilight Sky instead of Navy Blue?

The same difference applies the other way round: Twilight Sky is a little lighter, more muted, 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.