Cygnar Blue Base vs Imperial Blue

How close are they?

ΔE 17.4, loose: different enough that you should pick on purpose. Imperial Blue is much more muted, cooler than Cygnar Blue Base.

Can I use Imperial Blue instead of Cygnar Blue Base?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Imperial Blue is much more muted, cooler than Cygnar Blue Base.

Can I use Cygnar Blue Base instead of Imperial Blue?

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