ΔE 12.5, fair: the same colour family, but not a straight swap. Tarnished Brass is noticeably darker, more muted than Gehenna's Gold.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Tarnished Brass is noticeably darker, more muted than Gehenna's Gold.
The same difference applies the other way round: Gehenna's Gold is noticeably lighter, 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.
See Gehenna's Gold on the colour wheel See Tarnished Brass on the colour wheel
All matches: Gehenna's Gold equivalents · Tarnished Brass equivalents