How to change line color in line chart depending on values selected?

I need to dynamically change the line color in a line chart based on the data values selected. Specifically, I want to:

- Change color when values cross certain thresholds
- Update colors in real-time as data changes

The issue names no file, test, or entry point. Start by reviewing the line-chart implementation and its current color configuration, then establish how threshold-based and real-time updates should work; done means colors change correctly as selected values cross the defined thresholds.

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