Altdorf Guard Blue vs Eldar Robe

How close are they?

ΔE 8.4, close: similar, with a visible difference side by side. Eldar Robe is a little lighter, more saturated than Altdorf Guard Blue.

Can I use Eldar Robe instead of Altdorf Guard Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Eldar Robe is a little lighter, more saturated than Altdorf Guard Blue.

Can I use Altdorf Guard Blue instead of Eldar Robe?

The same difference applies the other way round: Altdorf Guard Blue is a little darker, 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.