ΔE 10.7, fair: the same colour family, but not a straight swap. Steel Legion Drab is noticeably darker, warmer than Reddish Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Steel Legion Drab is noticeably darker, warmer than Reddish Grey.
The same difference applies the other way round: Reddish Grey is noticeably lighter, 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 Steel Legion Drab on the colour wheel
All matches: Reddish Grey equivalents · Steel Legion Drab equivalents