ΔE 17.6, loose: different enough that you should pick on purpose. Zinc White is noticeably lighter, more muted than Ulthuan Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Zinc White is noticeably lighter, more muted than Ulthuan Grey.
The same difference applies the other way round: Ulthuan Grey is noticeably darker, more saturated.
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 Zinc White on the colour wheel
All matches: Ulthuan Grey equivalents · Zinc White equivalents