Standalone colorbar

[LecrisUT]

Is your feature request related to a problem? Please describe.

I am trying to plot a stacked line plot with a colorbar. I am able to construct it using the *= operator like:

            for t_ind, t_val in enumerate(curr_data["t"]):
                if t_ind % _skip != 0:
                    continue
                plot_data = curr_data.sel(t=t_val)
                plot_data = abs(plot_data)
                plot_data += _y_offset * (t_ind // _skip)
                overlay *= plot_data.hvplot(kind="line", x="x")
            overlay = overlay.opts(
                holoviews.opts.Curve(color=holoviews.Palette("Viridis")),
            )

The issue comes when I try to add colorbar=True either to .opts() or to .hvplot(), neither of which create the colorbar associated with it. On top of this, I would want to customize the position of the colorbar to be horizontal because I need it to span a layout of such plots

Describe the solution you'd like

Two features that would help here:

• Ability to use colorbar=true with line plots. Probably there is a bug that this is not possible
• Ability to create an independent colorbar that can be used with overlay *= or a layout

Describe alternatives you've considered

See #6355

[ahuang11]

Can you clarify what a colorbar for a line plot would look like?

[LecrisUT]

I might have cropped the plot in #6355, but basically it is for a stacked lineplot and the colorbar goes across the overlay's dimension, i.e. across the stack's offset.

[ahuang11]

I'm still somewhat confused what the colors in the colorbar would represent.

[LecrisUT]

I'm on mobile now, but consider this graph but with a semi-continuous transition. The colorbar would be a z-axis of time or applied laser strength, etc.