ΔE 15.1, loose: different enough that you should pick on purpose. Cerulean Blue Deep is noticeably darker, more muted than Celestium Blue. They are different kinds of paint: Citadel Celestium Blue is a one-coat contrast-style paint and Golden Cerulean Blue Deep is an opaque base/layer 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 15). Cerulean Blue Deep is noticeably darker, more muted than Celestium Blue. They are different kinds of paint.
The same difference applies the other way round: Celestium Blue is noticeably lighter, more saturated.
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 Celestium Blue on the colour wheel See Cerulean Blue Deep on the colour wheel
All matches: Celestium Blue equivalents · Cerulean Blue Deep equivalents