ΔE 12.2, fair: the same colour family, but not a straight swap. Amethyst is a little lighter, more saturated than Orchid.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Amethyst is a little lighter, more saturated than Orchid.
The same difference applies the other way round: Orchid is a little darker, 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.
See Orchid on the colour wheel See Amethyst on the colour wheel
All matches: Orchid equivalents · Amethyst equivalents