ΔE 13.6, fair: the same colour family, but not a straight swap. Granite Grey is a little lighter, more muted than Onyx Skin.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Granite Grey is a little lighter, more muted than Onyx Skin.
The same difference applies the other way round: Onyx Skin 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 Onyx Skin on the colour wheel See Granite Grey on the colour wheel
All matches: Onyx Skin equivalents · Granite Grey equivalents