ΔE 12.9, fair: the same colour family, but not a straight swap. Russ Grey is a little darker, more saturated than French Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Russ Grey is a little darker, more saturated than French Blue.
The same difference applies the other way round: French Blue 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 French Blue on the colour wheel See Russ Grey on the colour wheel
All matches: French Blue equivalents · Russ Grey equivalents