ΔE 10.9, fair: the same colour family, but not a straight swap. Medium Drab is a little darker, more saturated than RAF Dark Slate Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Medium Drab is a little darker, more saturated than RAF Dark Slate Grey.
The same difference applies the other way round: RAF Dark Slate Grey is a little lighter, more muted.
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 RAF Dark Slate Grey on the colour wheel See Medium Drab on the colour wheel
All matches: RAF Dark Slate Grey equivalents · Medium Drab equivalents