Iron Warriors vs Obsidian Black

How close are they?

ΔE 7.7, close: similar, with a visible difference side by side. Obsidian Black is more muted than Iron Warriors.

Can I use Obsidian Black instead of Iron Warriors?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Obsidian Black is more muted than Iron Warriors.

Can I use Iron Warriors instead of Obsidian Black?

The same difference applies the other way round: Iron Warriors is 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.