ΔE 18.9, loose: different enough that you should pick on purpose. Smoked Blue is noticeably darker, warmer than Fog Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Smoked Blue is noticeably darker, warmer than Fog Grey.
The same difference applies the other way round: Fog 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 Fog Grey on the colour wheel See Smoked Blue on the colour wheel
All matches: Fog Grey equivalents · Smoked Blue equivalents