Heavy Armour vs Old Gold

How close are they?

ΔE 17.6, loose: different enough that you should pick on purpose. Old Gold is a little lighter, much more saturated than Heavy Armour.

Can I use Old Gold instead of Heavy Armour?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Old Gold is a little lighter, much more saturated than Heavy Armour.

Can I use Heavy Armour instead of Old Gold?

The same difference applies the other way round: Heavy Armour is a little darker, much more muted.

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.