ΔE 11.3, fair: the same colour family, but not a straight swap. Clear Blue is a little darker, warmer than Royal Blue. They are different kinds of paint: Army Painter Royal Blue is an opaque base/layer paint and Reaper Clear Blue 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 11). Clear Blue is a little darker, warmer than Royal Blue. They are different kinds of paint.
The same difference applies the other way round: Royal Blue is a little lighter, 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 Clear Blue on the colour wheel
All matches: Royal Blue equivalents · Clear Blue equivalents