Royal Purple vs Lunar Eclipse

How close are they?

ΔE 19.8, loose: different enough that you should pick on purpose. Lunar Eclipse is a little darker, more muted, warmer than Royal Purple.

Can I use Lunar Eclipse instead of Royal Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Lunar Eclipse is a little darker, more muted, warmer than Royal Purple.

Can I use Royal Purple instead of Lunar Eclipse?

The same difference applies the other way round: Royal Purple is a little lighter, 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.