I was stuck on this problem for a while, I don't if someone has posted a solution already but it works for me if you do the following (it doesn't actually require SOUP):
- promote Cd from point to vertex
- delete any other attributes (except P, N, uv etc if needed)
- use the -rcs flag with the AbcImport mel command (and debug just in case), i.e.:
AbcImport -debug -rcs -mode import "path to alembic file.abc"
Then it should bring in the colour set and you should see the colours in the viewport