AE-9/AII Light Grey vs Ulthuan Grey

How close are they?

ΔE 11.2, fair: the same colour family, but not a straight swap. Ulthuan Grey is a little darker than AE-9/AII Light Grey.

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

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Ulthuan Grey is a little darker than AE-9/AII Light Grey.

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

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

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.