ΔE 9.0, close: similar, with a visible difference side by side. Frost is a little lighter, more saturated, cooler than Aethermatic Blue. They are different kinds of paint: Citadel Aethermatic Blue is a one-coat contrast-style paint and Vallejo Frost is a fluorescent or effect paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Frost is a little lighter, more saturated, cooler than Aethermatic Blue. They are different kinds of paint.
The same difference applies the other way round: Aethermatic Blue is a little darker, 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 Aethermatic Blue on the colour wheel See Frost on the colour wheel
All matches: Aethermatic Blue equivalents · Frost equivalents