Aeldari Emerald vs Cool Blue

How close are they?

ΔE 25.4, loose: different enough that you should pick on purpose. Cool Blue is much more muted, cooler than Aeldari Emerald.

Can I use Cool Blue instead of Aeldari Emerald?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Cool Blue is much more muted, cooler than Aeldari Emerald.

Can I use Aeldari Emerald instead of Cool Blue?

The same difference applies the other way round: Aeldari Emerald 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.