ΔE 9.6, close: similar, with a visible difference side by side. Clear Blue is a little darker, more saturated than Altdorf Guard Blue. They are different kinds of paint: Citadel Altdorf Guard Blue is an opaque base/layer paint and Reaper Clear Blue is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Clear Blue is a little darker, more saturated than Altdorf Guard Blue. They are different kinds of paint.
The same difference applies the other way round: Altdorf Guard Blue is a little lighter, 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.
See Altdorf Guard Blue on the colour wheel See Clear Blue on the colour wheel
All matches: Altdorf Guard Blue equivalents · Clear Blue equivalents