ΔE 15.1, loose: different enough that you should pick on purpose. Sky Grey is a little lighter, more muted than Stone Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Sky Grey is a little lighter, more muted than Stone Grey.
The same difference applies the other way round: Stone Grey is a little darker, 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 Stone Grey on the colour wheel See Sky Grey on the colour wheel
All matches: Stone Grey equivalents · Sky Grey equivalents