[Partition] hover tooltip shows incorrect nested colors

[nickofthyme]

Describe the issue

To Reproduce
Steps to reproduce the behavior:

1. Create a two layer sunburst chart
2. Set the fill color to progressively reduce alpha color
3. Hover over the smaller section of the chart slices
4. Notice some of the nested slices show the incorrect color, different than what is shown in the chart slice.
5. Go to the legend for the same value and notice the correct color is shown.

Expected behaviour
Tooltip colors show the correct color for nested slices.

Screenshots

Version (please complete the following information):

• Elastic Charts: latest

Kibana Cross Issues

elastic/kibana#203021