ΔE 15.6, loose: different enough that you should pick on purpose. Blue Glaze is a little lighter, warmer than Frostheart. They are different kinds of paint: Citadel Frostheart is a one-coat contrast-style paint and Two Thin Coats Blue Glaze is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Blue Glaze is a little lighter, warmer than Frostheart. They are different kinds of paint.
The same difference applies the other way round: Frostheart is a little darker, 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 Frostheart on the colour wheel See Blue Glaze on the colour wheel
All matches: Frostheart equivalents · Blue Glaze equivalents