Gehenna's Gold vs Top Brass

How close are they?

ΔE 21.6, loose: different enough that you should pick on purpose. Top Brass is noticeably lighter, more muted than Gehenna's Gold.

Can I use Top Brass instead of Gehenna's Gold?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Top Brass is noticeably lighter, more muted than Gehenna's Gold.

Can I use Gehenna's Gold instead of Top Brass?

The same difference applies the other way round: Gehenna's Gold is noticeably darker, 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.