Explore visual techniques for on-hover effects

For the on-hover effects in line plots, we change the color of the selected line. Currently this color is set by using the next color in the plot_config. Instead we should use a completely different color than what exists in the color palette.

Inspect the line-plot on-hover handling and how it currently selects the next color from plot_config. Trace the selected-line styling and verify that the completed behavior uses a distinct color outside the existing palette while preserving the other hover effects.

Written by the indexing model from the issue text.