Light Grey FS 36495 vs Ulthuan Grey

How close are they?

ΔE 6.3, close: similar, with a visible difference side by side. Ulthuan Grey is more saturated than Light Grey FS 36495.

Can I use Ulthuan Grey instead of Light Grey FS 36495?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Ulthuan Grey is more saturated than Light Grey FS 36495.

Can I use Light Grey FS 36495 instead of Ulthuan Grey?

The same difference applies the other way round: Light Grey FS 36495 is 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.