[Lens] break down by - allow users to select their color palette

[AlonaNadler]

Currently when breaking down by a field Lens uses the default color palette.
We would like to allow users to customize it by choosing from existing color palette

cc: @cchaos

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

There are two things that we should do for break down by in the short term, and one that we should delay on.

In the short term, "break down by" is always showing categorical data. Categorical data should be displayed using distinct colors for each category, and should not be displayed using a continuous scale. For example, the default colors we use in Visualize are categorical:

So the two things we should do in the short term are:

1. Let users assign a color to a specific category. For example, Kibana Airways can be purple. This can be done like Visualize already does:

2. Allow creation of categorical palettes from Lens, or wait for this to be supported in all of Kibana: color palettes that can be used across Kibana applications #43697

The thing to delay is continuous color palettes for Break Down by. There will be a future where users can break down by a continuous value, but we are not there yet.

[wylieconlon]

Was not aware that charts had already done some work on this: elastic/elastic-charts#51

[wylieconlon]

Summarizing some offline discussions I've had about categorical palettes in Lens:

• This is not just about XY charts, I expect that pie charts will have the same color options
• Lens is using a good default, the EUI palette.
• Because the EUI palette is new, Lens stands out in dashboards. Sometimes users want dashboards to be cohesive, so Lens should support the default kibana palette as one of the categorical palettes.
• For similar reasons, Lens should support a muted style such as grayscale or shades of blue as a categorical palette.
  • A common feature of these muted palettes is a highlight color such as magenta to make one series stand out
• Lens should also support custom categorical palettes, using the same implementation as the Maps app:

• One difference that Lens could start doing is saving the custom palettes for future use- or using previously saved palettes. color palettes that can be used across Kibana applications #43697

[wylieconlon]

Based on the latest discussions we will be placing this in the chart-level Lens settings for the first iteration, as opposed to being in a specific dimension. This is because both XY and pie charts need to have categorical colors, and placing it in a specific dimension does not work for pie charts.

[flash1293]

I would like to propose to postpone this after the "Lens by default" timeframe and go with #68404 instead. The difference is instead of having a color palette setting for the "break down by" dimension, there is a chart level setting for the same thing.

For most cases this will behave in the same way, but it solves the case if the user doesn't have a "break down by" dimension yet and wants to change the used palette (e.g. when using multiple metrics). The only cost of that I can think of is that multiple layers will use the same palette, but I don't think this would be a big impact.

Besides that, it simplifies implementation by quite a bit because we don't have to take care of a bunch of edge cases when working with multiple layers (less bugs and easier to maintain).

cc @AlonaNadler @cchaos

[flash1293]

Closed by #75309