ΔE 19.6, loose: different enough that you should pick on purpose. True Brass is noticeably lighter, more muted, cooler than Old Gold.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). True Brass is noticeably lighter, more muted, cooler than Old Gold.
The same difference applies the other way round: Old Gold is noticeably darker, more saturated, warmer.
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 Old Gold on the colour wheel See True Brass on the colour wheel
All matches: Old Gold equivalents · True Brass equivalents