ΔE 39.1, loose: different enough that you should pick on purpose. Gloss Varnish is noticeably lighter, much more muted than Nihilakh Oxide.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 39). Gloss Varnish is noticeably lighter, much more muted than Nihilakh Oxide.
The same difference applies the other way round: Nihilakh Oxide is noticeably darker, much 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 Nihilakh Oxide on the colour wheel See Gloss Varnish on the colour wheel
All matches: Nihilakh Oxide equivalents · Gloss Varnish equivalents