ΔE 8.5, close: similar, with a visible difference side by side. Ulthuan Grey is a little lighter, more saturated than Light Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Ulthuan Grey is a little lighter, more saturated than Light Grey.
The same difference applies the other way round: Light Grey is a little darker, 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 Light Grey on the colour wheel See Ulthuan Grey on the colour wheel
All matches: Light Grey equivalents · Ulthuan Grey equivalents