Copper Coin vs Arcane Gold

How close are they?

ΔE 16.8, loose: different enough that you should pick on purpose. Arcane Gold is noticeably lighter, more muted than Copper Coin.

Can I use Arcane Gold instead of Copper Coin?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Arcane Gold is noticeably lighter, more muted than Copper Coin.

Can I use Copper Coin instead of Arcane Gold?

The same difference applies the other way round: Copper Coin 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.