ΔE 12.0, fair: the same colour family, but not a straight swap. Cerulean Blue Hue is a little darker, more saturated, warmer than Royal Blue. They are different kinds of paint: Army Painter Royal Blue is an opaque base/layer paint and Golden Cerulean Blue Hue is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Cerulean Blue Hue is a little darker, more saturated, warmer than Royal Blue. They are different kinds of paint.
The same difference applies the other way round: Royal Blue is a little lighter, more muted, 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 Royal Blue on the colour wheel See Cerulean Blue Hue on the colour wheel
All matches: Royal Blue equivalents · Cerulean Blue Hue equivalents