Crystal Blue vs Braineater Azure

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Braineater Azure is more muted, warmer than Crystal Blue.

Can I use Braineater Azure instead of Crystal Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Braineater Azure is more muted, warmer than Crystal Blue.

Can I use Crystal Blue instead of Braineater Azure?

The same difference applies the other way round: Crystal Blue is more saturated, 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.