Dark Silver vs Brass

How close are they?

ΔE 37.5, loose: different enough that you should pick on purpose. Brass is noticeably darker, much more saturated than Dark Silver.

Can I use Brass instead of Dark Silver?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 37). Brass is noticeably darker, much more saturated than Dark Silver.

Can I use Dark Silver instead of Brass?

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