ΔE 16.2, loose: different enough that you should pick on purpose. Arianrhod Blue is a little darker, warmer than Frostveil.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Arianrhod Blue is a little darker, warmer than Frostveil.
The same difference applies the other way round: Frostveil is a little lighter, 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 Frostveil on the colour wheel See Arianrhod Blue on the colour wheel
All matches: Frostveil equivalents · Arianrhod Blue equivalents