ΔE 7.4, close: similar, with a visible difference side by side. Orange Brown is a little lighter, warmer than Flat Earth.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Orange Brown is a little lighter, warmer than Flat Earth.
The same difference applies the other way round: Flat Earth is a little darker, cooler.
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.
See Flat Earth on the colour wheel See Orange Brown on the colour wheel
All matches: Flat Earth equivalents · Orange Brown equivalents