ΔE 16.4, loose: different enough that you should pick on purpose. Medium Olive is a little lighter, much more saturated than Slate Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Medium Olive is a little lighter, much more saturated than Slate Grey.
The same difference applies the other way round: Slate Grey is a little darker, much 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 Slate Grey on the colour wheel See Medium Olive on the colour wheel
All matches: Slate Grey equivalents · Medium Olive equivalents