Dark Brown vs Earth Clay

How close are they?

ΔE 6.9, close: similar, with a visible difference side by side. Earth Clay is a little lighter, more muted than Dark Brown.

Can I use Earth Clay instead of Dark Brown?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Earth Clay is a little lighter, more muted than Dark Brown.

Can I use Dark Brown instead of Earth Clay?

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