WWI French Brown vs Flat Earth

How close are they?

ΔE 9.7, close: similar, with a visible difference side by side. Flat Earth is a little lighter, warmer than WWI French Brown.

Can I use Flat Earth instead of WWI French Brown?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Flat Earth is a little lighter, warmer than WWI French Brown.

Can I use WWI French Brown instead of Flat Earth?

The same difference applies the other way round: WWI French Brown 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.