Power Blue vs Calth Blue Clear

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Calth Blue Clear is much more saturated, warmer than Power Blue.

Can I use Calth Blue Clear instead of Power Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Calth Blue Clear is much more saturated, warmer than Power Blue.

Can I use Power Blue instead of Calth Blue Clear?

The same difference applies the other way round: Power Blue is much more muted, cooler.

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.