Cerulean Blue Deep vs Royal Blue

How close are they?

ΔE 9.4, close: similar, with a visible difference side by side. Royal Blue is a little lighter, more saturated than Cerulean Blue Deep.

Can I use Royal Blue instead of Cerulean Blue Deep?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Royal Blue is a little lighter, more saturated than Cerulean Blue Deep.

Can I use Cerulean Blue Deep instead of Royal Blue?

The same difference applies the other way round: Cerulean Blue Deep is a little 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.