Cerulean Blue, Chromium vs Royal Blue

How close are they?

ΔE 23.4, loose: different enough that you should pick on purpose. Royal Blue is noticeably darker, much more muted than Cerulean Blue, Chromium.

Can I use Royal Blue instead of Cerulean Blue, Chromium?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Royal Blue is noticeably darker, much more muted than Cerulean Blue, Chromium.

Can I use Cerulean Blue, Chromium instead of Royal Blue?

The same difference applies the other way round: Cerulean Blue, Chromium is noticeably lighter, much 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.