Ashen Stone vs Blue Glacier

How close are they?

ΔE 22.3, loose: different enough that you should pick on purpose. Blue Glacier is a little darker, much more saturated than Ashen Stone.

Can I use Blue Glacier instead of Ashen Stone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Blue Glacier is a little darker, much more saturated than Ashen Stone.

Can I use Ashen Stone instead of Blue Glacier?

The same difference applies the other way round: Ashen Stone is a little lighter, much more muted.

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.