True Brass vs Iridescent Gold (Coarse)

How close are they?

ΔE 28.6, loose: different enough that you should pick on purpose. Iridescent Gold (Coarse) is noticeably lighter, warmer than True Brass. They are different kinds of paint: Army Painter True Brass is a metallic and Golden Iridescent Gold (Coarse) is a pearl paint, so they won’t behave the same on the model even where the colour is close.

Can I use Iridescent Gold (Coarse) instead of True Brass?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Iridescent Gold (Coarse) is noticeably lighter, warmer than True Brass. They are different kinds of paint.

Can I use True Brass instead of Iridescent Gold (Coarse)?

The same difference applies the other way round: True Brass is noticeably darker, cooler.

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.