[Feature] not to reassign series colors

[helgasoft]

What problem does this feature solve?

We start with some series with default colors (unassigned).
When one series color is programmatically set, the other series colors auto-update - Demo.
It seems more like a bug to me, but lets call it a Feature since no one has complained about it yet.

What does the proposed API look like?

Make sure not to alter other series when only one is updated. It creates confusion in the chart.