ΔE 9.7, close: similar, with a visible difference side by side. USAF Light Gray is a little darker than Ulthuan Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). USAF Light Gray is a little darker than Ulthuan Grey.
The same difference applies the other way round: Ulthuan 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.
See Ulthuan Grey on the colour wheel See USAF Light Gray on the colour wheel
All matches: Ulthuan Grey equivalents · USAF Light Gray equivalents