ΔE 26.6, loose: different enough that you should pick on purpose. Eau de Nil “D.E.G.” is much more muted than Plague Toad Venom.
Can I use Eau de Nil “D.E.G.” instead of Plague Toad Venom?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Eau de Nil “D.E.G.” is much more muted than Plague Toad Venom.
Can I use Plague Toad Venom instead of Eau de Nil “D.E.G.”?
The same difference applies the other way round: Plague Toad Venom is 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.