Gorthor Brown vs Overlord Olive

How close are they?

ΔE 18.5, loose: different enough that you should pick on purpose. Overlord Olive is noticeably darker, more muted, cooler than Gorthor Brown.

Can I use Overlord Olive instead of Gorthor Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Overlord Olive is noticeably darker, more muted, cooler than Gorthor Brown.

Can I use Gorthor Brown instead of Overlord Olive?

The same difference applies the other way round: Gorthor Brown is noticeably lighter, more saturated, 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.