ΔE 13.0, fair: the same colour family, but not a straight swap. Sky Grey is a little lighter, more muted than Gravestone Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Sky Grey is a little lighter, more muted than Gravestone Blue.
The same difference applies the other way round: Gravestone Blue 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 Gravestone Blue on the colour wheel See Sky Grey on the colour wheel
All matches: Gravestone Blue equivalents · Sky Grey equivalents