ΔE 19.5, loose: different enough that you should pick on purpose. Amethyst Purple is noticeably darker, more muted, cooler than Romeo/Juliet.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Amethyst Purple is noticeably darker, more muted, cooler than Romeo/Juliet.
The same difference applies the other way round: Romeo/Juliet is noticeably lighter, more saturated, warmer.
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.
See Romeo/Juliet on the colour wheel See Amethyst Purple on the colour wheel
All matches: Romeo/Juliet equivalents · Amethyst Purple equivalents