Royal Cloak vs Dragon Blue

How close are they?

ΔE 29.6, loose: different enough that you should pick on purpose. Dragon Blue is noticeably darker, much more muted, warmer than Royal Cloak.

Can I use Dragon Blue instead of Royal Cloak?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Dragon Blue is noticeably darker, much more muted, warmer than Royal Cloak.

Can I use Royal Cloak instead of Dragon Blue?

The same difference applies the other way round: Royal Cloak is noticeably lighter, much more saturated, 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.