Ultramarine Blue vs Bismark's Grave

How close are they?

ΔE 25.9, loose: different enough that you should pick on purpose. Bismark's Grave is a little lighter, much more muted, cooler than Ultramarine Blue.

Can I use Bismark's Grave instead of Ultramarine Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Bismark's Grave is a little lighter, much more muted, cooler than Ultramarine Blue.

Can I use Ultramarine Blue instead of Bismark's Grave?

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