Blue Licks vs Ultramarine Blue

How close are they?

ΔE 23.6, loose: different enough that you should pick on purpose. Ultramarine Blue is noticeably darker, much more muted than Blue Licks.

Can I use Ultramarine Blue instead of Blue Licks?

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

Can I use Blue Licks instead of Ultramarine Blue?

The same difference applies the other way round: Blue Licks is noticeably lighter, much 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.