ΔE 7.6, close: similar, with a visible difference side by side. Ivory Tusk is a little lighter, cooler than Bony Spikes.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Ivory Tusk is a little lighter, cooler than Bony Spikes.
The same difference applies the other way round: Bony Spikes is a little darker, 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 Bony Spikes on the colour wheel See Ivory Tusk on the colour wheel
All matches: Bony Spikes equivalents · Ivory Tusk equivalents