Ultramar Blue vs Azure

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Azure is more saturated, warmer than Ultramar Blue.

Can I use Azure instead of Ultramar Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Azure is more saturated, warmer than Ultramar Blue.

Can I use Ultramar Blue instead of Azure?

The same difference applies the other way round: Ultramar Blue is 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.