Moonpetal vs Red Purple

How close are they?

ΔE 15.8, loose: different enough that you should pick on purpose. Red Purple is noticeably darker, more saturated than Moonpetal.

Can I use Red Purple instead of Moonpetal?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Red Purple is noticeably darker, more saturated than Moonpetal.

Can I use Moonpetal instead of Red Purple?

The same difference applies the other way round: Moonpetal is noticeably lighter, 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.