Dark Brown vs Muddy Ground

How close are they?

ΔE 16.6, loose: different enough that you should pick on purpose. Muddy Ground is a little darker, much more muted than Dark Brown.

Can I use Muddy Ground instead of Dark Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Muddy Ground is a little darker, much more muted than Dark Brown.

Can I use Dark Brown instead of Muddy Ground?

The same difference applies the other way round: Dark Brown is a little lighter, much 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.