[TSVB] Background color doesn't render correctly on timeseries

[stratoula]

Kibana version:
v7.90+

Elasticsearch version:
v7.90+

Browser version:
Chrome 83.0.4103.61

Describe the bug:
On timeseries when the user chooses the background color to not be transparent, a border is added but the bg color of the chart remains transparent.
Steps to reproduce:

1. Open TSVB timeseries
2. Change the background color
3. Check that it is not applied to the chart

Expected behavior:
The background color is applied to the chart

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[stratoula]

@markov00 I think it has to do with the es-charts. The background color is applied but is not rendered correctly. Does it ring a bell? Maybe we should change the configuration on the timeseries vis.

[nickofthyme]

Yes most definitely, I'll look into this issue this morning. Thanks @stratoula