Dark Wood vs Black Legion

How close are they?

ΔE 28.8, loose: different enough that you should pick on purpose. Black Legion is noticeably darker, much more muted than Dark Wood.

Can I use Black Legion instead of Dark Wood?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Black Legion is noticeably darker, much more muted than Dark Wood.

Can I use Dark Wood instead of Black Legion?

The same difference applies the other way round: Dark Wood is noticeably lighter, 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.