Aethermatic Blue vs Skull Linen

How close are they?

ΔE 26.6, loose: different enough that you should pick on purpose. Skull Linen is a little darker, much more muted than Aethermatic Blue.

Can I use Skull Linen instead of Aethermatic Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Skull Linen is a little darker, much more muted than Aethermatic Blue.

Can I use Aethermatic Blue instead of Skull Linen?

The same difference applies the other way round: Aethermatic 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.