Runefang Steel vs Bitz O'Tin

How close are they?

ΔE 19.3, loose: different enough that you should pick on purpose. Bitz O'Tin is noticeably darker, more saturated than Runefang Steel.

Can I use Bitz O'Tin instead of Runefang Steel?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Bitz O'Tin is noticeably darker, more saturated than Runefang Steel.

Can I use Runefang Steel instead of Bitz O'Tin?

The same difference applies the other way round: Runefang Steel is noticeably lighter, 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.