ΔE 42.4, loose: different enough that you should pick on purpose. Amethyst is noticeably lighter, much more saturated, cooler than Sunset Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 42). Amethyst is noticeably lighter, much more saturated, cooler than Sunset Purple.
The same difference applies the other way round: Sunset Purple is noticeably darker, much more muted, 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 Sunset Purple on the colour wheel See Amethyst on the colour wheel
All matches: Sunset Purple equivalents · Amethyst equivalents