ΔE 11.2, fair: the same colour family, but not a straight swap. Medium Sea Gray 2 (RAF) is a little darker than Ulthuan Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Medium Sea Gray 2 (RAF) 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 Medium Sea Gray 2 (RAF) on the colour wheel
All matches: Ulthuan Grey equivalents · Medium Sea Gray 2 (RAF) equivalents