ΔE 9.8, close: similar, with a visible difference side by side. Flat Brown is more muted, cooler than Red Rage.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Flat Brown is more muted, cooler than Red Rage.
The same difference applies the other way round: Red Rage is 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.
See Red Rage on the colour wheel See Flat Brown on the colour wheel
All matches: Red Rage equivalents · Flat Brown equivalents