ΔE 10.5, fair: the same colour family, but not a straight swap. Slate Grey is a little darker, more muted than Steel Legion Drab.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Slate Grey is a little darker, more muted than Steel Legion Drab.
The same difference applies the other way round: Steel Legion Drab is a little lighter, more saturated.
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 Steel Legion Drab on the colour wheel See Slate Grey on the colour wheel
All matches: Steel Legion Drab equivalents · Slate Grey equivalents