ΔE 8.0, close: similar, with a visible difference side by side. Tyrant Skull is a little lighter, more saturated, cooler than Old Bone.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Tyrant Skull is a little lighter, more saturated, cooler than Old Bone.
The same difference applies the other way round: Old Bone is a little darker, more muted, 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 Old Bone on the colour wheel See Tyrant Skull on the colour wheel
All matches: Old Bone equivalents · Tyrant Skull equivalents