Castellax Bronze vs Dark Iron

How close are they?

ΔE 27.9, loose: different enough that you should pick on purpose. Dark Iron is noticeably darker, much more muted than Castellax Bronze.

Can I use Dark Iron instead of Castellax Bronze?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Dark Iron is noticeably darker, much more muted than Castellax Bronze.

Can I use Castellax Bronze instead of Dark Iron?

The same difference applies the other way round: Castellax Bronze 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.