Aztec Gold vs Radium

How close are they?

ΔE 18.7, loose: different enough that you should pick on purpose. Radium is noticeably lighter, more muted, warmer than Aztec Gold.

Can I use Radium instead of Aztec Gold?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Radium is noticeably lighter, more muted, warmer than Aztec Gold.

Can I use Aztec Gold instead of Radium?

The same difference applies the other way round: Aztec Gold is noticeably darker, more saturated, 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.