ΔE 7.5, close: similar, with a visible difference side by side. Khaki Brown is a little lighter, more saturated, warmer than Reddish Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Khaki Brown is a little lighter, more saturated, warmer than Reddish Grey.
The same difference applies the other way round: Reddish Grey is a little darker, more muted, 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 Reddish Grey on the colour wheel See Khaki Brown on the colour wheel
All matches: Reddish Grey equivalents · Khaki Brown equivalents