Dark Green Brown vs Military Yellow

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Military Yellow is a little lighter, more saturated, warmer than Dark Green Brown.

Can I use Military Yellow instead of Dark Green Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Military Yellow is a little lighter, more saturated, warmer than Dark Green Brown.

Can I use Dark Green Brown instead of Military Yellow?

The same difference applies the other way round: Dark Green Brown is a little darker, more muted, 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.