Ultramarine Violet vs Blueberry

How close are they?

ΔE 8.4, close: similar, with a visible difference side by side. Blueberry is a little darker than Ultramarine Violet.

Can I use Blueberry instead of Ultramarine Violet?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Blueberry is a little darker than Ultramarine Violet.

Can I use Ultramarine Violet instead of Blueberry?

The same difference applies the other way round: Ultramarine Violet is a little lighter.

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.