ΔE 12.1, fair: the same colour family, but not a straight swap. Altdorf Guard Blue is more saturated, cooler than Twilight Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Altdorf Guard Blue is more saturated, cooler than Twilight Purple.
The same difference applies the other way round: Twilight Purple is 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 Twilight Purple on the colour wheel See Altdorf Guard Blue on the colour wheel
All matches: Twilight Purple equivalents · Altdorf Guard Blue equivalents