ΔE 13.4, fair: the same colour family, but not a straight swap. Willow Bark is noticeably darker, more muted than Werewolf Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Willow Bark is noticeably darker, more muted than Werewolf Brown.
The same difference applies the other way round: Werewolf Brown is noticeably lighter, 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 Werewolf Brown on the colour wheel See Willow Bark on the colour wheel
All matches: Werewolf Brown equivalents · Willow Bark equivalents