Etherium Blue vs Cool Grey

How close are they?

ΔE 20.3, loose: different enough that you should pick on purpose. Cool Grey is a little darker, much more muted than Etherium Blue.

Can I use Cool Grey instead of Etherium Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Cool Grey is a little darker, much more muted than Etherium Blue.

Can I use Etherium Blue instead of Cool Grey?

The same difference applies the other way round: Etherium Blue is a little lighter, much more saturated.

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.