ΔE 19.6, loose: different enough that you should pick on purpose. Obsidian Black is a little lighter, much more muted than Sparkling Amethyst.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Obsidian Black is a little lighter, much more muted than Sparkling Amethyst.
The same difference applies the other way round: Sparkling Amethyst is a little darker, much more saturated.
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 Sparkling Amethyst on the colour wheel See Obsidian Black on the colour wheel
All matches: Sparkling Amethyst equivalents · Obsidian Black equivalents