ΔE 19.7, loose: different enough that you should pick on purpose. Fluorescent Blue is noticeably lighter, much more saturated than Imrik Blue. They are different kinds of paint: Citadel Imrik Blue is an opaque base/layer 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 20). Fluorescent Blue is noticeably lighter, much more saturated than Imrik Blue. They are different kinds of paint.
The same difference applies the other way round: Imrik Blue is noticeably darker, much 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 Imrik Blue on the colour wheel See Fluorescent Blue on the colour wheel
All matches: Imrik Blue equivalents · Fluorescent Blue equivalents