ΔE 9.6, close: similar, with a visible difference side by side. Smoke Gray is a little lighter, more muted than Onyx Skin.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Smoke Gray 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 Smoke Gray on the colour wheel
All matches: Onyx Skin equivalents · Smoke Gray equivalents