Battle of Marathon vs Cavalry Brown

How close are they?

ΔE 16.6, loose: different enough that you should pick on purpose. Cavalry Brown is a little darker, more saturated, cooler than Battle of Marathon.

Can I use Cavalry Brown instead of Battle of Marathon?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Cavalry Brown is a little darker, more saturated, cooler than Battle of Marathon.

Can I use Battle of Marathon instead of Cavalry Brown?

The same difference applies the other way round: Battle of Marathon is a little lighter, more muted, 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.