Royal Robes vs Legacy Blue

How close are they?

ΔE 27.7, loose: different enough that you should pick on purpose. Legacy Blue is noticeably darker, much more muted, warmer than Royal Robes.

Can I use Legacy Blue instead of Royal Robes?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Legacy Blue is noticeably darker, much more muted, warmer than Royal Robes.

Can I use Royal Robes instead of Legacy Blue?

The same difference applies the other way round: Royal Robes 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.