Cygnar Blue Base vs Ultramarine Blue

How close are they?

ΔE 24.5, loose: different enough that you should pick on purpose. Ultramarine Blue is noticeably lighter, much more muted, cooler than Cygnar Blue Base.

Can I use Ultramarine Blue instead of Cygnar Blue Base?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Ultramarine Blue is noticeably lighter, much more muted, cooler than Cygnar Blue Base.

Can I use Cygnar Blue Base instead of Ultramarine Blue?

The same difference applies the other way round: Cygnar Blue Base is noticeably darker, 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.