Ultramarine Blue vs Caledor Sky

How close are they?

ΔE 9.1, close: similar, with a visible difference side by side. Caledor Sky is a little darker, more muted than Ultramarine Blue.

Can I use Caledor Sky instead of Ultramarine Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Caledor Sky is a little darker, more muted than Ultramarine Blue.

Can I use Ultramarine Blue instead of Caledor Sky?

The same difference applies the other way round: Ultramarine Blue is a little lighter, more saturated.

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.