ΔE 9.8, close: similar, with a visible difference side by side. Tyrant Skull is a little darker, cooler than Quartz Skin.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Tyrant Skull is a little darker, cooler than Quartz Skin.
The same difference applies the other way round: Quartz Skin is a little lighter, warmer.
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 Quartz Skin on the colour wheel See Tyrant Skull on the colour wheel
All matches: Quartz Skin equivalents · Tyrant Skull equivalents