Eidolon Grey vs Concrete

How close are they?

ΔE 6.3, close: similar, with a visible difference side by side. Concrete is a little lighter, more muted than Eidolon Grey.

Can I use Concrete instead of Eidolon Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Concrete is a little lighter, more muted than Eidolon Grey.

Can I use Eidolon Grey instead of Concrete?

The same difference applies the other way round: Eidolon Grey is a little darker, 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.