Gorthor Brown vs Red Brown

How close are they?

ΔE 9.2, close: similar, with a visible difference side by side. Red Brown is a little darker, more muted than Gorthor Brown.

Can I use Red Brown instead of Gorthor Brown?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Red Brown is a little darker, more muted than Gorthor Brown.

Can I use Gorthor Brown instead of Red Brown?

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