ΔE 7.1, close: similar, with a visible difference side by side. Relic Blue is a little darker, more saturated than Frostheart. They are different kinds of paint: Citadel Frostheart is a one-coat contrast-style paint and Two Thin Coats Relic Blue is an opaque base/layer 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 7). Relic Blue is a little darker, more saturated than Frostheart. They are different kinds of paint.
The same difference applies the other way round: Frostheart is a little lighter, 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.
See Frostheart on the colour wheel See Relic Blue on the colour wheel
All matches: Frostheart equivalents · Relic Blue equivalents