Calgar Blue vs Bright Blue

How close are they?

ΔE 17.0, loose: different enough that you should pick on purpose. Bright Blue is a little darker, much more saturated, warmer than Calgar Blue.

Can I use Bright Blue instead of Calgar Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Bright Blue is a little darker, much more saturated, warmer than Calgar Blue.

Can I use Calgar Blue instead of Bright Blue?

The same difference applies the other way round: Calgar Blue is a little lighter, 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.