ΔE 10.8, fair: the same colour family, but not a straight swap. Pastel Blue is a little lighter, more muted, warmer than Ahriman Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Pastel Blue is a little lighter, more muted, warmer than Ahriman Blue.
The same difference applies the other way round: Ahriman Blue is a little darker, more saturated, cooler.
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 Ahriman Blue on the colour wheel See Pastel Blue on the colour wheel
All matches: Ahriman Blue equivalents · Pastel Blue equivalents