Ultramar Blue vs Blue

How close are they?

ΔE 11.3, fair: the same colour family, but not a straight swap. Blue is a little darker, more muted than Ultramar Blue.

Can I use Blue instead of Ultramar Blue?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Blue is a little darker, more muted than Ultramar Blue.

Can I use Ultramar Blue instead of Blue?

The same difference applies the other way round: Ultramar 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.