Black Templar vs Willow Bark

How close are they?

ΔE 9.0, close: similar, with a visible difference side by side. Willow Bark is a little lighter, more saturated than Black Templar.

Can I use Willow Bark instead of Black Templar?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Willow Bark is a little lighter, more saturated than Black Templar.

Can I use Black Templar instead of Willow Bark?

The same difference applies the other way round: Black Templar is a little darker, more muted.

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.