ΔE 18.0, loose: different enough that you should pick on purpose. Fluorescent Blue is noticeably lighter, more saturated than Frostheart. They are different kinds of paint: Citadel Frostheart is a one-coat contrast-style paint and Golden Fluorescent Blue is a fluorescent or effect 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 18). Fluorescent Blue is noticeably lighter, more saturated than Frostheart. They are different kinds of paint.
The same difference applies the other way round: Frostheart is noticeably darker, 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 Fluorescent Blue on the colour wheel
All matches: Frostheart equivalents · Fluorescent Blue equivalents