ΔE 10.8, fair: the same colour family, but not a straight swap. Ulthuan Grey is a little lighter, more saturated than Stone 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 lighter, more saturated than Stone Grey.
The same difference applies the other way round: Stone 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 Stone Grey on the colour wheel See Ulthuan Grey on the colour wheel
All matches: Stone Grey equivalents · Ulthuan Grey equivalents