ΔE 14.2, fair: the same colour family, but not a straight swap. IJA Gray is much more saturated than Typhon Ash.
Can I use IJA Gray instead of Typhon Ash?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). IJA Gray is much more saturated than Typhon Ash.
Can I use Typhon Ash instead of IJA Gray?
The same difference applies the other way round: Typhon Ash is much more muted.
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.