[highlight] Borealis lighter colors are not so visible

[markov00]

Describe the issue
With the introduction of the new Borealis color palette, the chart series highlighter does not work effectively. When hovering over a light-colored series, the "highlight" is barely visible because the other series are only slightly dimmed, making it difficult to distinguish the hovered series from the rest.

Possible Solutions

• Increase the dimming effect on non-hovered series.
• Introduce an additional outline or glow effect for the hovered series.
• Adjust contrast dynamically based on the hovered series’ color.

To Reproduce
Steps to reproduce the behavior:

1. Use a chart with multiple series in the new Borealis color palette.
2. Hover over a series with a lighter color.
3. Observe that the highlight effect is minimal, making it hard to differentiate the hovered series.

Expected behaviour
The hovered series should stand out clearly against the dimmed background, ensuring better visibility and focus.

Screenshots

Screen.Recording.2025-02-19.at.10.00.26.mp4

Additional context
This issue is particularly noticeable with lighter colors in the Borealis palette. Improving the highlight mechanism would enhance usability and readability.

Errors in browser console
N/A

Checklist

• The proper chart type label has been added (e.g. :xy, :partition)
• The proper feature labels have been added (e.g. :interactions, :axis)
• Every related Kibana issue is listed under Kibana Cross Issues list and the kibana cross issue tag is applied

[nickofthyme]

Yeah I noticed it is not easy to always clear what, especially for gradients. Sometimes the highlight is nearly the same color as an adjacent geom.

I think we rethink the highlight strategy altogether.