Blue vs Ultramarine Blue

How close are they?

ΔE 14.5, fair: the same colour family, but not a straight swap. Ultramarine Blue is a little lighter, more muted than Blue.

Can I use Ultramarine Blue instead of Blue?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Ultramarine Blue is a little lighter, more muted than Blue.

Can I use Blue instead of Ultramarine Blue?

The same difference applies the other way round: Blue is a little darker, 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.