ΔE 12.8, fair: the same colour family, but not a straight swap. Ivory Tusk is more muted than Terminatus Stone.
Can I use Ivory Tusk instead of Terminatus Stone?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Ivory Tusk is more muted than Terminatus Stone.
Can I use Terminatus Stone instead of Ivory Tusk?
The same difference applies the other way round: Terminatus Stone is 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.