AE-9/AII Light Grey vs Decal Softener

How close are they?

ΔE 6.0, close: similar, with a visible difference side by side. Decal Softener is a little lighter than AE-9/AII Light Grey.

Can I use Decal Softener instead of AE-9/AII Light Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Decal Softener is a little lighter than AE-9/AII Light Grey.

Can I use AE-9/AII Light Grey instead of Decal Softener?

The same difference applies the other way round: AE-9/AII Light Grey is a little darker.

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.