`generic.text.color()` has a small range

When testing ssg on the `star_080223` schema, I got errors from the `UNIQUE` (though, non-PK) constraint on `advance_decision_type.care_code`. It turns out that there aren't that many colours...

A couple of options come to mind:

1. We could consider this a good thing since it highlights the fact that we don't handle unique constraints very cleverly (we ignore them) and open an issue to handle them better.
2. We could switch to `generic.text.words(5)` or similar.