Blue Raspberry vs Ultramarine Blue

How close are they?

ΔE 15.0, loose: different enough that you should pick on purpose. Ultramarine Blue is much more muted, cooler than Blue Raspberry.

Can I use Ultramarine Blue instead of Blue Raspberry?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Ultramarine Blue is much more muted, cooler than Blue Raspberry.

Can I use Blue Raspberry instead of Ultramarine Blue?

The same difference applies the other way round: Blue Raspberry is much more saturated, 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.