Ultramarine Blue vs Twilight Sky

How close are they?

ΔE 8.3, close: similar, with a visible difference side by side. Twilight Sky is more saturated, cooler than Ultramarine Blue.

Can I use Twilight Sky instead of Ultramarine Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Twilight Sky is more saturated, cooler than Ultramarine Blue.

Can I use Ultramarine Blue instead of Twilight Sky?

The same difference applies the other way round: Ultramarine Blue is more muted, 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.