On D9, using Billboard and Views, with only one data field, we can get a multiple colors chart (one color for each value, for example on a donut or a pie), see screenshot.
On Drupal 10, when using the same View to create a chart, there is only one color for the data field with no options to modify it, see screenshot.
Looking at Charts configuration we have multiple colors on default display but they seem not to be used by Views, see screenshot.
You can try the patch here ( https://www.drupal.org/project/charts/issues/3493686 🐛 Billboard and C3 not using custom colors for Pie or Donut charts Active ), but I think that might not be the final solution.