Crystal Blue vs Blue Licks

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Blue Licks is noticeably lighter, more saturated than Crystal Blue.

Can I use Blue Licks instead of Crystal Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Blue Licks is noticeably lighter, more saturated than Crystal Blue.

Can I use Crystal Blue instead of Blue Licks?

The same difference applies the other way round: Crystal Blue is noticeably darker, more muted.

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.