Gorthor Brown vs US Field Drab

How close are they?

ΔE 9.2, close: similar, with a visible difference side by side. US Field Drab is a little lighter, cooler than Gorthor Brown.

Can I use US Field Drab instead of Gorthor Brown?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). US Field Drab is a little lighter, cooler than Gorthor Brown.

Can I use Gorthor Brown instead of US Field Drab?

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